No need to upgrade. The problem can be found in the file vpnclient.ini, probably located in the directory "C:\Program Files\Cisco Systems\VPN Client".
There are probably som really high values in the logwindX and logwindowy values. Just delete these lines and start the client again.
/Jonas
Thanks Jonas
No high values in logwindX and logwindY but very high values in these lines:
WindowX=4294935296
WindowY=4294935296
When deleting them it solves my problem. Thanks!!!!