For me it's sound like you somehow have messed up your configuration or are having a hardware problem.
upgrade to 1.2.3 http://blog.pfsense.org/?p=377
http://snapshots.pfsense.org/FreeBSD7/RELENG_1_2/
But in the end I would bet that reinstall will be a better approach.
Might help http://pfsense.site88.net/multiwan.html