This issue caused an absolute nightmare. Basically we have a site created using site template around 20 of them. In all of that only a site collection administrator could upload the document and didn’t get access denied.
But for any one with Contribute or site owners rights experienced access denied when clicking on Add Document or Upload Document/s.
ULS is the way to go does give a hint and resolved this for us.
Created a new site using the same site template and didn’t see an error
On this new site Publishing and Content Organizer features were not activated but on the other 20 odd sites, this feature was activated were we experienced the issue of access denied.
Site Template didn’t contain publishing and content organizer features in it. This bemused me it worked initially but found that we recently installed Service Pack 1 and June 2011 Cumulative update. Thought this might be causing it but any ways to resolve this
Deactivated Publishing Feature
Deactivated Content Organizer
Deactivated and re-activated Enterprise Feature
Deactivated and re-activated Standard Feature
Boom issue resolved.
This issue occurred for us due to SP 1 and June 2011 CU. I would say always check in ULS logs for more information on why the issue is occuring.