Compilation errors with ImageResizer 3.2.1 - imageresizer

Question

After allowing Nuget to update ImageResizer 3.1.5 to version 3.2.1 my compiles are failing with multiple errors (all same type):
Error 5 Missing compiler required member 'System.Runtime.CompilerServices.ExtensionAttribute..ctor'
Apparently this is the result of an assembly version mismatch. Deleting all ImageResizer references in the project allows an error-free compile.
Reverting to ImageResizer 3.1.5 also allows a successful compilation.
My project is a simple MVC3 application targeting .NET4 - both ImageResizer 3.1.5 and 3.2.1 are targeting v2.0.50727
Any ideas on how this could be fixed?
Thanks in anticipation!

Answer 1

Update (Jun 20th 2012): The best solution is for the project to roll back extension method support. ImageResizer 3.2.2 will no longer offer extension methods, but some of the functionality will be duplicated in the ResizeSettings and Instructions classes to minimize breakage for those who have already coded against the new alpha APIs.
ImageResizer V4 will most likely require .NET 3.5, and will re-introduce the missing features.
Update: please see this question instead if you have any solutions to this catch-22.
I apologize for the issues.
I'm still trying to gather data and discover a long-term solution, but this is what I have so far:
Workaround A:
In Solution Explorer, expand the References folder in your project, select ImageResizer, and go to Properties. Change the Aliases field from 'global' to 'ir'.
Workaround B:
Set your project to use .NET 2.0, save, then revert it back to using .NET 3.5 or .NET 4.
Workaround C:
Manually remove your System.Core reference and add the correct one back. (The usual culprit is an upgraded project with a System.Core 3.0 reference in a 3.5 project). On ASP.NET, you can do this in web.config.
Workaround D:
Revert to 3.2.0, but only if you're using C#.
Why this is happening
VisualStudio/MSBuild find multiple definitions of System.Runtime.CompilerServices.ExtensionAttribute in the project during compilation, but instead of picking the public copy defined in System.Core, the compiler decides to use the internal, assembly-local copy defined in ImageResizer.dll. Then it complains because other assemblies can't reach it. Inane.
What should happen
Microsoft has used this technique several times in the past without issues, and it's widely documented. The compiler is supposed to pick the public instance for project-wide use, but instead it's picking the 'internal' copy. And this isn't affecting many developers; and only a few can reproduce it with a new project.
Public vs. Internal
V2.3.0 defined ExtensionAttribute as public instead of internal. This caused a compile-timer error in VB projects, but not in C# projects. I immediately released 2.3.1 with it marked internal, but I'm now seeing problems with C# projects instead. Catch-22 here.
It works for other people... and Microsoft! Why me?
http://www.danielmoth.com/Blog/Using-Extension-Methods-In-Fx-20-Projects.aspx
http://www.codethinked.com/using-extension-methods-in-net-20
http://kohari.org/2008/04/04/extension-methods-in-net-20/
Using extension methods in .NET 2.0?
The 'hack' was even featured in MSDN magazine.
How you can help
I need more data to completely figure this out. If you're experiencing the issue, please e-mail a .zip file of the project to support#imageresizing.net, and include your VisualStudio/.NET version numbers (Go to Visual Studio, Help, About, and click Copy Info, then paste it into the e-mail).
Hopefully I'll be able to find the exact circumstance(s) that trigger the problem.
Update - just found this article which implies the only solution is creating multiple versions of the assembly. But Microsoft didn't! What am I missing? Also, NuGet doesn't support 2.0 vs 3.5 versioning, so unless I can find a single-assembly solution I might have to drop 2.0 support.