table permissions

Hi everybody,
I have a table called 'set' and I am trying to edit or insert an entry
there. I made sure that I have ALL permissions to modify that table, but
still I get the same error:
ERROR: activity: Permission denied.

I don't know where 'activity' part came from, but there is a reference
to activity table in set table.
I know this is a very vague descritption of the symptoms, but I don't
know where to look to find out more info. I'll happily provide any
further details.
thanks,

Oleg