One of our clients hit an unusual problem when trying to schedule a Report using Reporting Services 2000.
The error was:
EXECUTE permission denied on object 'sp_add_category', database 'msdb', owner 'dbo'.
It turns out that this system stored procedure is used to add jobs to the SQL Server Agent.
The procedure is only available to members of the sysadmin role or the db_owner role in the MSDB database.
I have advised him to try adding the account reporting services service is running under to the MSDB Database as a member of the DB_owners role even though the message seems to be implying that execution is being denied too the dbo user! (I know not the most locked down solution but one that is viable in the enviroment). For a fuller listing of Reporting Services permissions this post seems to be a comprehensive list even though it does not specify if it relates to SQL 2000 or 2005.
I will edit this when I get feedback on the effects of my idea.