While working on a rather large BizTalk 2010 project I came across this very strange behaviour and wanted to post a solution to it here in case anyone else may experience this.
When attempting to open an orchestration in the orchestration designer within Visual Studio 2010, I noticed the orchestration opened in text only view and I was unable to view the orchestration designer. This was for one orchestration only, all other orchestrations in the project opened properly. The project also compiled properly without any errors. I right-clicked on the affected orchestration and choose Open With -> BizTalk Orchestration Designer. I also clicked Set as Default. I could then view the orchestration in design mode as expected. However upon closing and re-opening the solution, I noticed that once again the orchestration was opening in a text only view.
I then opened the .btproj file in a text editor and noticed the following (this is a snippet of my .btproj file):
<ItemGroup>
<XLang Include="OrderCancel.odx">
<TypeName>OrderCancel</TypeName>
<Namespace>MyNamespace.Orchestrations</Namespace>
<SubType>Designer</SubType>
</XLang>
</ItemGroup>
<ItemGroup>
<XLang Include="OrderModify.odx">
<TypeName>OrderModify</TypeName>
<Namespace>Mynamespace.Orchestrations</Namespace>
</XLang>
</ItemGroup>
Note the tag:
<SubType>Designer</SubType>
I simply removed the SubType tag, saved the .btproj file and reopened the solution in Visual Studio and the orchestration opened normally again.