Is it possible to build multiple configurations at the same time in visual basic express edition 2008?

As far as I know, I can't build multiple configs at once within a visual studio express edition, but I have tried with msbuild and a vbproj file, with limited success:

<Target Name="Build">
  <MSBuild Projects="solution1.sln" Properties="Configuration=Debug;Platform=Any CPU" />
  <MSBuild Projects="solution1.sln" Properties="Configuration=Release;Platform=Any CPU" />
  <MSBuild P开发者_运维百科rojects="solution1.sln" Properties="Configuration=Custom;Platform=Any CPU" />
</Target>

This happily compiles the 1st two standard configurations, but fails at Custom with the message:

"The specified configuration "Custom|Any CPU" is invalid. Please specify a valid ..."

Note that the Custom configuration compiles fine within visual studio.

Any ideas why it's failing?