Rules In Error problem

Platform: Outlook 2k on Win2k.

I have been building a list of rules to help filter junk mail. For
this I take two approaches.

First, I have a rule named "Junk Subject Lines (client only)" that
reads "Apply this rule after message arrives with 'aaa' or 'bbb' or
'ccc' in the subject permanantly delete it."

Second, I have several rules for checking the message header. A
typical rule here is named "chat.ru" and reads "Apply this rule after
message arrives with chat.ru in the message header permanently delete
it." Since this type of rule only allows one character string for
comparison (unlike when checking the subject line) I am getting quite
a list of these.

Now, the problem is that several times a day I get a Rules in Error
pop-up. The error is always either 'You do not have sufficient
permission . . . ' or 'Cannot remove messages from the folder.' When
this happens, I find these rules unchecked, but if I run them manually
(Rules Wizard | Run Rules Now) the msgs that got missed get processed
properly.

Does anyone have an explanation for why this happens and what I can do
to fix it? A search of the ng archives didn't turn up anything
useful.

Thanks.