I've got the latest xwis connection tool, but
keep getting a message about my serial number being
temporarily banned. I don't know why it would be.

Here is the Test output from the tool:

server: 62.93.200.61
nick: biloreily
: 375 u :- Login to XCC Online failed!
: 372 u :-
: 372 u :- Strike Team: http://strike-team.net/
: 372 u :-
: 372 u :- Your serial number has been temporarily banned. Visit Strike Team for more information (SID: 11221).
: 376
: 607

Same result with 2 other nicks.