I had the same problem and fixed it like this:
I've downloaded change set 49753 (this should be version 188.8.131.52) and compiled it - it showed this error. Then I've downloaded change set 54863 and copied all the cs files from the DocX directory to the DocX directory of the 184.108.40.206 version. After compiling
it worked for me.
Looks like the problem got fixed with change set 54863, but it can't be compiled in VS 2008, because the solution format already got changed to the VS2010 format.