I have a WP-MU site configured using subdomains: *.universal-nexus.com
I have a file: Jake's Last Mission.png
It uploads fine, to some of the blogs. To others it gives an HTTP error.
After nearly going absolutely mad trying to fix permissions and figure out if a plugin was getting in the way I fixed it by renaming the file: JakesLastMission.jpeg (I'd converted it previously because some thing suggested PNG files are wont to cause the error). That worked.
Why on the same installation of WordPress would the filename be a problem on one blog, but not the other?