The tools version "12.0" is unrecognized. Available tools versions are "2.0", "3.5", "4.0"

08/04/2015 13:36

The tools version "12.0" is unrecognized. Available tools versions are "2.0", "3.5", "4.0"

this error occured when project was created in Visual Studio 2013 and moved and opened in Visual Studio 2010.

Workaround is to replace ToolsVersion attribute in csproj file with e. g. 4.0.