Synchronizing calendar caused iCal error message

Hello!
I hope somebody can help me to solve this…it’s probably really easy but I can’t solveit. I try to sync up my gmail calendar with iCal but I am facing the following server error message:
"The Server responded with an error
The request for account “[email protected]” failed.
The server responded with
“HTTP/1.1 401 Unauthorized”
to operation CalDAVAccountRefreshQueueableOperation."
Then I pressed OK and the server error message showed again. Click OK and iCal quits. Then back to the starting. I have pulled iCal from my finder into scrap and installed again from my Mac Operating System X Install DVD with possible Installs, but the same problem happens.
Need your help. Any help greatly appreciated. Thanks in advance.
