So I have my VS 2010 and also just installed VS 2012. After that my main project started showing this error:

“The ‘VSTS for Database Professionals Sql Server Data-tier Application’ package did not load correctly”

And also some other errors about components I have never heard before.

This solution provided by Eric Lee worked for me.

Even though the author intended it for a slightly different set of actions.
Short version (copied from the above website):

1. Locate your Visual Studio 2010 installation media.
2. In the \WCU\DAC folder, you’ll find three MSIs: DACFramework_enu.msi, DACProjectSystemSetup_enu.msi, and TSqlLanguageService_enu.msi. Run and install each of them.
3. Reapply Visual Studio 2010 SP1.

Thanks, Eric!