We just upg from 2.4 to 2.6. The install errored because the themes change in 2.6. So I went to the 2.4 instance, changed theme to standard, exported DB and did the upg. Now when I try to change the default theme it doesn't change in the list or on the site. Also when I tried to upload a new theme, that errored also.
On windows 2008x64 IIS 7.5