When trying to build a Visual Studio solution (sln) file, you get this error:
MyProject.sln(2): Solution file error MSB5014: File format version is not recognized. MSBuild can only read solution files between versions 7.0 and 9.0, inclusive.
This is because you are using the wrong version of msbuild.exe. You may already have the correct version installed, but the PATH environment variable is set to point the command prompt to run the wrong one. Adjust the path variable to point to another version, such as the version that comes with .NET 3.5 or 4.0. Search for copies of msbuild.exe on your PC to get the exact paths.