I just ran across this, I'll see if it works.
http://www.moviecodec.com/topics/3588p3.html
"regsvr32 /u shmedia.dll " Fixed the problem.
Simply do the following steps:
1) Open a command window (Start->Run, type in 'cmd' hit enter)
2) To remove image preview, type and hit enter
regsvr32 /u shimgvw.dll
3) To readd image preview, type and hit enter
regsvr32 shimgvw.dll
4) To remove media preview, type and hit enter
regsvr32 /u shmedia.dll
5) To readd media preview, type and hit enter
regsvr32 shmedia.dll