Hi,
The upload problems are when using the Image Gallery or other features?
The posted error looks like a database problem rather than an upload problem, though it may be happening at upload time.
The Image Gallery does not enforce any quotas so I would expect no difference for one user vs another but when uploading from within the editor ie using the image toolbar to browse server and upload there are file system quotas enforced that seem a likely factor if admins get different results. For that kind of problem see the config settings at the bottom of this article, copy those from web.config and paste them in user.config to customize them.
For the database error, can you reproduce it? if so please tell me steps and I'll look into it.
See also supporting large file uploads.
Hope that helps,
Joe