We had the same problem, WAS occassionally failing to start and claiming the same port conflict. A netstat -an showed that the conflict was bogus. We tried using the "more compatible" SOAP port and sometimes it worked, sometimes it didn't. Neither of those should have come into play anyways - there was no conflict and no firewall to consider since we were launching server and development locally through Rational Software Architect. To make things more frustrating, it would sometimes start up and sometimes not. Very inconsistent.
It turned out that the server was trying to find itself using the machine's old Windows Network/host name - we had changed it sometime after installing WAS.
Our short-term kludge was to put the old host name into the machine's local c:\winnt\system32\drivers\etc\hosts file with its current address.
The real answer was probably to reinstall WAS, but it seemed kind of silly to have to reinstall just because the host name changed.