Fax transaction unable to stop itself

I have used the windows fax for about 1 year. recently the fax process start
having problems. Sometimes the Fax monitor say "Fax completed successfully"
but it never jump to the next transaction. So next morning when I come, this
transaction has been proceesed for 711 minutes and keep going but the status
is completed. the other transactions just keep waiting. Then I have to stop
it manually but after that the Windows Fax will be frozen and need to restart
the whole windows.


How can I solve this problem?