I have no clue if Codeplex mundged this up or if something else is a problem but I wanted to give my fix steps for correcting the repository corruption I seem to be getting 100% of the time.
First is cloning this properly. Be sure to use the advanced clone option called "Use uncompressed transfer". The end result is a repo set at revision -1.
Fix #1 - revision 3
1) Clone a separate instance to revision 2. I called this funq.fixed.
2) Download the Silverlight Toolkit December 2008 from here http://silverlight.codeplex.com/releases/view/19172#DownloadId=51431
3) Add Microsoft.Silverlight.Testing.dll and Microsoft.VisualStudio.QualityTools.UnitTesting.Silverlight.dll. to the the directory src\Lib\Silverlight UT. Commit.
4) Now the fun part. Go into the hg directory .hg\store\data\src_lib_silverlight _u_t\ and look for _microsoft._silverlight._testing.dll.i. Copy this to the main funq repository in the exact same location.
5) Edit .hg\store\fncache and the line data/src/Lib/Silverlight UT/Microsoft.Silverlight.Testing.dll.i (I did mine underneath the existing entry for *Testing.dll.d)
6) Update to revision 53 to prepare for fix #2
Fix #2 - Revision 54
1) Clone a copy of the fixed main repository up to revision 53 in a separate directory called funq.fixed2.
2) Update Microsoft.Silverlight.Testing.dll from the April 2010 Silverlight Toolkit in src\Lib\Silverlight UT. Commit.
3) Go into the hg directory .hg\store\data\src_lib_silverlight _u_t\ and this time grab both _microsoft._silverlight._testing.dll.d and _microsoft._silverlight._testing.dll.i (the only difference is the .i and .d on the end) and paste BOTH FILES back to the same location in the main repository
4) Now update to revision 54 and then to the latest revision and you should be set. I had to do this due to some file mismatches.
This only matters for those of us that wish to fix their local repository. Going forward I should be able to see any updates. If you'd like, I can send you my repository if somehow your local version is corrupt. Unfortunately I don't think codeplex can be fixed as easily but perhaps with these steps we could help them out?