I have this same problem. It's been driving me crazy because I know its a permission problem looking at the logs.
The funny thing is that I don't have the problem on my test server, which is an exact duplicate of the online site. The only difference between the two is that the online site has an SSL certificate on it.
EDIT: Actually there is one other difference between the test server and my online site. The test server and the SQL test server are running on the same machine, whereas the online site and the online SQL are running on separate virtual machines. The problem for us seems to be a permission problem between the web machine and the SQL machine according to the SQL server logs. This shows up as a failed SQL login for account SQLREPORT, which is not any login that we have associated with either the website or with the SQL login.
Hopefully someone out there can shed a little light on this and help with a fix.