http://bugs.winehq.org/show_bug.cgi?id=22521
--- Comment #12 from Austin English austinenglish@gmail.com 2010-04-29 11:09:08 --- Created an attachment (id=27616) --> (http://bugs.winehq.org/attachment.cgi?id=27616) working install log
Works for me with winetricks. Didn't test it though.
Can you try a silent install (winetricks -q dotnet20sp2).