Hi Stefan.
I know the procedure but, this is not the problem, my program is configured in .NET MF 4.2, this is what is confusing me.
I have found that changing the target to 4.1 (or below) saving and closing the properties, then changing the target back to 4.2 has fixed that issue for me in the past.
I suspect that it forces a regeneration of the relevant sections in the *.csproj file so that correct references are loaded etc.
You can determine if the issue is with your project file by creating a new project targeting 4.2 and deploying blinky or something equally trivial, if it works then its your project file is at fault and the procedure above should fix it, if not then it would probably be the SDK's, so a full uninstall and reinstall should tidy everything up.
Nak.