Is your site on a server farm? I noticed I could upload with browsers *other* than Firefox and IE, but the resulting pages did not always contain the latest data. That can happen on a server farm, because each server has its own cached copy of gallery objects.
The next version of GSP (2.4) will contain a configuration setting to disable caching to help in scenarios like this, but there aren't any good options for now (short of editing the code to purge the cache on every page load, which is what one person did). 2.4 will be out by the end of the year.
I can't say for sure the upload problem is related to the server farm, but it is a good bet. The caching issue will probably be your biggest problem, but there is a workaround to get uploading working: Change the site to work in medium trust, which forces GSP to use a standard ASP.NET FileUpload control. To do this, open web.config in a text editor and look for this line:
Code:<!-- <trust level="Full" /> -->
Change it to this:
Code:<trust level="Medium" />
Roger Martin
Creator and Lead Developer of Gallery Server Pro