Owin error with ASP.NET MVC application

Question

I have an ASP.NET application that runs fine on my local machine. I just uploaded it to a server using web deploy. I'm getting the following error when I try to view the site:

The following errors occurred while attempting to load the app. - The OwinStartup attribute discovered in assembly 'Gators3' referencing startup type 'Gators3.Startup' conflicts with the attribute in assembly 'MyFirstProject2' referencing startup type 'MyFirstProject2.Startup' because they have the same FriendlyName ''. Remove or rename one of the attributes, or reference the desired type directly. To disable OWIN startup discovery, add the appSetting owin:AutomaticAppStartup with a value of "false" in your web.config. To specify the OWIN startup Assembly, Class, or Method, add the appSetting owin:AppStartup with the fully qualified startup class or configuration method name in your web.config.

I tried searching the entire solution for the string "MyFirstProject2" but did not come up with anything. The message gives a couple of suggestions, but none of them mean anything to me. I don't know how to "Remove or rename one of the attributes, or reference the desired type directly," and I don't see a place in the web.config to "add the appSetting owin:AppStartup with the fully qualified startup class or configuration method name in your web.config."

I found this, but am not quite sure how to implement it. I also did find [assembly: OwinStartupAttribute(typeof(Gators3.Startup))] in my Startup.cs, but not sure what the right thing to do there is either.

Possible Duplicate : http://stackoverflow.com/questions/21701297/error-when-renaming-asp-net-mvc-5-application — Farhan S., Oct 03 '15 at 10:23
I had the same problem, just on a single dev box, after I renamed the project. Nishamth's answer worked for me. — PeteH, Jun 26 '19 at 18:17

LaoR · Answer 1 · 2015-07-31T10:15:00.553

The problem is that the Gators3.dll and MyFirstProject2.dll are in the same folder (I guess it is bin folder on your server) and both are using Owin middleware. If you do not need MyFirstProject2.dll then the easiest way would be to delete that assembly. If you need it, but without Owin - add following line to Web.config/app.config in your MyFirstProject2 project: <add key="owin:AutomaticAppStartup" value="False" />

If you need to use Owin for two projects configure friendly names for both of them.

Gators3 project:

Change Owin startup attribute to something like:

 attribute [assembly: OwinStartupAttribute("GatorsConfig", typeof(Gators3.Startup))]

And add following line to Web.config within appSettings section:

   <add key="owin:appStartup" value="GatorsConfig" />

MyFirstProject2 project:

Change Owin startup attribute to something like:

   attribute [assembly: OwinStartupAttribute("MyFirstProject2Config", typeof(MyFirstProject2.Startup))]

And add following line to Web.config within appSettings section:

   <add key="owin:appStartup" value="MyFirstProject2Config" />

Nishanth Shaan · Answer 2 · 2022-11-14T19:00:10.003

28

I had the same issue : removing everything in the /bin folder and rebuilding the solution alone worked for me. But it could be combined with renaming your assembly attribute at the top of the startupclass, giving it a Firendly name which will help to differentiate both the startup files.

[assembly: OwinStartup("MyFriendlyNameForProject1",typeof(MyProject.Startup))]

edited Nov 14 '22 at 19:00

answered Sep 19 '15 at 09:42

Nishanth Shaan

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Manually ensuring `/bin` folder is cleaned (=delete all files), was the key to me (thx). Renaming assembly, "cleaning" from within VS and rebuilding is not enough, since the clean will not be able to know about the legacy dll's, since these still have the same old name – Frederik Struck-Schøning Apr 15 '16 at 12:25
Manually ensuring /bin folder is cleaned is fully solution – Sultan Dec 25 '20 at 20:15

score 25 · Answer 3 · answered Jan 02 '17 at 09:57

25

Clear your bin folder and obj folder.Rebuild the project again and run :)

answered Jan 02 '17 at 09:57

Sriman Saswat Suvankar

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Just clearing the bin folder didn't help alone, i had to also clear the obj folder. thanks – Jeffrey Holmes Mar 07 '17 at 12:01
Worked for me. I thought this was what "Clean Solution" was supposed to do? – Steve Smith May 08 '19 at 12:44
There are times when 'clean solution' doesn't clear all the contents in the concerned folders. I can't say exactly what but this happened to me when I was messing with assembly names. – Nishanth Shaan Oct 17 '22 at 08:37

score 7 · Answer 4 · answered May 24 '18 at 10:43

7

Also, if you publish a solution to Azure:

1) right click and select Publish.
2) go to Settings and expand the "File Publish Options"
3) select "Remove additional files at destination"
4) Publish

Worked for me, after deleting the files from obj and bin Folder.

answered May 24 '18 at 10:43

Michael Staples

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This could be the solution independent of publish destination (Azure, IIS, IISExpress, etc.). – Mikael Gyth Jun 12 '18 at 08:26
@Michael Staples Thank God for people like you. Saved my day. – FreedomOfSpeech Aug 30 '18 at 00:04

score 6 · Answer 5 · answered Mar 09 '17 at 10:10

6

Delete anything that says 'MyFirstProject2' from your bin folder and rebuild the solution, It will work.

answered Mar 09 '17 at 10:10

Tino Jose Thannippara

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well this works for me. no more additional configurations needed. I just clear up the bin folder. and then rebuild and it works like magic.. – Tsuna Sawada Jul 11 '19 at 14:19

score 4 · Answer 6 · answered Aug 22 '17 at 14:10

4

Happens when you reference (by mistake?) a project with owin startup inside another project with owin startup. Fix - delete the reference, bin, obj folders and rebuild.

answered Aug 22 '17 at 14:10

Nick Kovalsky

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Thank you very much, This should be the accepted answer! – Gertjan Gielen May 03 '18 at 14:32

score 3 · Answer 7 · answered Apr 27 '18 at 09:50

3

I had the same problem and i added the following tag on web config:

<appSettings>
    <add key="owin:AutomaticAppStartup" value="false" />
</appSettings>

answered Apr 27 '18 at 09:50

Võ Đại Thắng

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This worked for me! I also deleted before the bin and obj folders of all projects in the solution, and updated the package with the code: "Update-Package Microsoft.AspNet.WebApi -reinstall" – Sterling Diaz Jul 11 '18 at 15:13
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If **false** - public static void InitialiseThis(**HttpApplication** application) is called, when **true** public static void Configuration(**IAppBuilder** app/*, IServiceCollection services*/) – Jan Sep 05 '20 at 09:44

score 2 · Answer 8 · answered Jun 27 '18 at 07:42

2

This is what I have done:

Since I have 3 projects in one solution, I had to open all bin folder of each project and delete all files there.
Build each project one by one.
Build the whole solution.

Problem solves on my part.

answered Jun 27 '18 at 07:42

Willy David Jr

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score 2 · Answer 9 · answered Apr 02 '19 at 04:01

2

Remove all files in your 'bin' folder and rebuild.

answered Apr 02 '19 at 04:01

Sudheer Muhammed

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score 1 · Answer 10 · answered Oct 24 '18 at 16:04

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Delete files Bin, Build each project one by one.

answered Oct 24 '18 at 16:04

Jimmy Santillan

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Can you develop more your answer to make it more helpful? – FrankS101 Oct 24 '18 at 16:23

score 1 · Answer 11 · answered Feb 25 '19 at 21:03

1

Deleted everything in the bin folder, including the roslyn folder then published, and everything worked fine.

answered Feb 25 '19 at 21:03

George Williams

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score 0 · Answer 12 · edited Jan 18 '19 at 08:31

0

Remove old built data in temporary files, in the following path

C:\Users\[user]\AppData\Local\Temp\Temporary ASP.NET Files\vs

edited Jan 18 '19 at 08:31

Andrei Dragotoniu

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answered Jan 18 '19 at 07:37

mosi98

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score 0 · Answer 13 · answered Sep 07 '22 at 17:40

0

In my case, I was referencing one project in the other accidentally, which is why I was getting this error after removing the one accidentally added in the main project solved the problem.

answered Sep 07 '22 at 17:40

Munam Yousuf

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Owin error with ASP.NET MVC application

13 Answers13