Sebastian, I think I have found a bug in the control that only allows the SuperUser account to upload. When it uploads to the Temp or Main folder it does a IsInRole check to see if it has "Write" perms. When I was debugging I noticed that the writeRoles (see below) was always "" (even tho Admin and Reg Users have read and write on my folders).
Dim writeRoles As String = GetRoles(root + UploadFolder, settings.PortalId, "WRITE")
The SuperUser ignores the Folder Role perms and always returns true, hence they can always upload, but a normal admin cannot.
The reason it is blank is because it is passing the whole root and Folder name into the GetRoles method whereas the Folder dictionary is stored as FolderName only (with a "\" on the end). Hence it was looking for "F:\DotNetNuke_4.3.1_Source\Website\Portals\POKER\Leagues" in the Folder dic but not finding it (it is stored as "Leagues\" in this example.
Here is the fix but I am curious as to why this was not spotted before - perhaps I have configured it wrong earlier in the process? Have you tried uploading with any role other than Host?
Dim writeRoles As String = GetRoles(UploadFolder + "/", settings.PortalId, "WRITE")