Invalid code coverage item error in MSTest

I ran into the following running unit tests after a build under TFS 2010:

Invalid code coverage item: The pdb file name must contain at least one character.

I had modified the .testsettings file to use relative paths instead of absolute paths, but the build was failing with the above error.

The solution was to edit the .testsettings file to add a pdbFile attribute:

<CodeCoverageItem binaryFile="..\Utilities\%outdir%\Utilities.dll" pdbFile="..\Utilities\%outdir%\Utilities.pdb" instrumentInPlace="true" />