Thank you for providing us with the log file.
Looking at it, I see that the error is provoked by the fact that Sitefinity is trying to create a stored procedure in the SQL database. This action, of course, requires higher grants than select/execute.
Sitefinity does not create the stored procedure each time it starts up. Having that said, the problem you experience might be occuring because:
1. You have more than one application tied with the same database. If you have more that one Sitefinity instance with the same database, please make sure they are all upgraded to the same version. Otherwise, what might happen is that one application downgrades the database, while the other one upgrades it. The stored procedures are created/changed only during the database upgrade/creation.
2. If you have upgraded the project files only, the first time when you run Sitefinity after the upgrade, the CMS will try to create the stored procedure. Assuming the user is limited when comes to permissions, this could be an expected behavior. Once the the upgrade (database upgrade as well) is over, you can set back the limited permissions for the database account.
Let us know if this is the case.
the Telerik team