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I am trying to create a webservice where the functions are performed by a 64 bit DLL. When I try to build this service i get the error "An attempt was made to load a program with an incorrect format." But when I run a 32 bit DLL it works fine.

I am trying to run in a visual studio 2012 on .net 4 framework in C#

I have tried changing the app pool settings in IIS and changed build platform target to any cpu. Cannot identify where the problem is coming from. Please provide you assistance. Thank you

snab
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  • **Related post** - [What are the pros and cons of running IIS as 32bit vs 64bit on a 64bit OS?](https://stackoverflow.com/q/507820/465053) – RBT Apr 17 '18 at 06:08

3 Answers3

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Right click on the application pool you are using and go to Advanced Settings. Under (General) there is a setting called Enable 32-Bit Applications. If you're running on a 64 bit OS and this is set to true then the app-pool will be a 32bit process, and therefore your 64bit DLL won't load. Set it to false to make your app-pool a 64bit process.

Also, check the dependencies of the DLL you're building as 64bit. It may be using a 32bit dll/assembly. If you've got any [DllImport] attributes in your code then look at the .dlls they refer to and ensure they're 64bit compatible.

Sean
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If your web service references 64 bit dlls it must be compiled to x64

user995219
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Try not to mix AnyCPU compilation with 32 or 64 bit DLL (DLL can be compiled as 32bit or 64bit or both) - behavior will depend on platform and in some environments it will work, in some not.

GregS
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  • Thank you GregS, But i have changed it to x64 – snab Jan 21 '14 at 12:07
  • what have you changed? target platform in VS? or IIS settings? - i got the same issue few years ago, proper compilation settings helped, also try to specify target framework in config file - "supportedRuntime" and "requiredRuntime". You said, that 32bit dll works but 64 not - even if the compilation target framework is set to x64? – GregS Jan 21 '14 at 13:02
  • target platform in VS and Enable 32-Bit Applications to False. the 32 bit does not run when changed to x64 – snab Jan 21 '14 at 13:08