really cant say with the little information you have provided.
this is no reason i can think of.
what are your tab parameters?
what are your cb user parameters (in the tab when in edit mode?)?
ok - i was wrong ... all other users worked just fine before... now the users where i have changed settings for upload to 15mb don't work either and changing the settings back does not affect that fact that they don't work anymore.. all really strange.. will reinstall... or do u want to have a quick look first?
Took a quick look with the info you sent via PM.
Upload works just fine for all users.
The files are stored in their plugin gallery location.
For some reason when you are trying to retrieve them (or link to them) you are not allowed.
Has something changed with your host?
Maybe htaccess changes?
To conclude - the plugin is working just fine.
Reinstalling will not help.
Something else is happening.