> I have a few clients with lists that are getting this error: "You do not
> own any lists on this server" when logging into the web interface to
> manage their lists.

Check the configuration and make SURE if their names follow the 
address in the Owner=  field, that there is at least one space 
following the address. 

Then have them select "Log out" on any page. This will remove any 
cookie which may be storing an incorrect address. Then have them 
access the List Mgt page again. They will need to login with their 
owner's address and PW. 

> One list in particular has about 20 owners. Is there a limit to the
> number of owners any given list can have?

No

> Another list is brand new and listed with one owner and when they log
> int it gives the same error "You do not own any lists on this server".
> 
> I have double and tripple checked the spelling of each email address.
> 
> Is there a solution/workaround to this problem? It seems to be happenign
> more frequently now.

I bet it is the no space problem in the Owner= field. The interface 
when no space is present appears like there is one, so double check 
it.