The AsyncCTP is getting a bit long in the tooth. This post is to explain how, why, and what to do.
Common symptoms:
AsyncCTP fails to install -- i.e. it doesn't create the "Async CTP" folder inside "My Documents", and VS doesn't recognize the async keywords.
Installing VS11 causes AsyncCTP to stop working.
AsyncCTP doesn't work on Windows 8.
Explanation
The AsyncCTP is an update. It updates Visual Studio 2010 with modified versions of the VS IDE compilers that colorize the new keywords. It also updates the .NET4 framework with modified versions of the command-line csc.exe and vbc.exe compilers. But the AsyncCTP was never incorporated into Microsoft's official source code for VS2010 or .NET4, and was never meant to be -- it's just an experimental CTP.
And so, when Microsoft produces official updates to either VS or .NET4, and they touch the same files, then they tend to overwrite the AsyncCTP -- or prevent it from installing in the first place.
Also .NET45, which comes with VS11 and Win8, is an in-place update on top of .NET4, and so replaces the csc.exe and vbc.exe from the AsyncCTP with updated ones. As Stephen Toub explains, the new csc.exe and vbc.exe are incompatible with AsyncCTPLibrary.dll.
What to do
Best option is to upgrade to VS11 Beta and .NET45. It has much better async support (fewer bugs, more features, better debugging, better perf)
Failing that, if you're stuck with VS2010 + AsyncCTP, here are ideas:
If you already have VS2010 + AsyncCTP working, then don't install VS11.
If you have VS2010 SP1 but the AsyncCTP installer doesn't seem to have worked, the problem might be conflicting updates such as
KB2635973, KB2615527, KB2645410
Any update after October 11 is liable to conflict, though. Go to ControlPanel > AddRemovePrograms > WindowsUpdates and uninstall them if present.
Platforms:
Targeting .NET45 with async:
you have to use VS11 Beta, which works fine.
Read more: Lucian's VBlog
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