Running Cisco VPN client on a wireless connection

Hi, I’ve a secured wireless connection using D-link router. When I run cisco VPN client,
it connects, but the internet connection is lost immediately (in 3 seconds). If I connect
ethernet cable, VPN and internet connection
works fine (no issue). NOTE: The “lost connection” happens for all wireless networks I tried (4 different places).

It appears there is some conflict between
wireless connection and Cisco VPN client connection. There should be some configuration
setting on wireless router or VPN client which should fix this issue, but can’t figure it out.
I tried disabling PPTP and changing MTU sizes, but no luck.

Please help. Thanks very much.

Some info:
Windows XP Home SP2
Cisco VPN client 4.6.03.0021