When using matrix configuration, the parameters are not properly given to msbuild.
It seems that it automatically generates command line arguments for msbuild which is a great idea but the syntax is not good.

For instance if I add an axis "Configuration" with values "Debug" and "Release".
It will generate the command line :
cmd.exe /C C:\Windows\Microsoft.NET\Framework\v4.0.30319\msbuild.exe -P:Configuration=Release -P:Platform=Win32

The correct syntax would be (notice the "/p" instead of "-P") :
cmd.exe /C C:\Windows\Microsoft.NET\Framework\v4.0.30319\msbuild.exe /p:Configuration=Release /p:Platform=Win32"
as indicated here : http://msdn.microsoft.com/en-us/library/ms164311.aspx