Vista - Remote Desktop Connection issue

Hi

I'm connecting work desktop from home laptop thru vpn connection. Both home & work computers are windows vista. (working from home)

My problem is : I'm able to do VPN to workplace, but when I try to connect work computer thru Remote Desktop Connection I'm getting following error:

This conmputer can't connect to the remote computer. Try connecting
again. If the problem continues, contact the owner of the remote computer or
yur network administrator."

But If I ask (by calling) one of my work colleage to reboot my work desktop, it is allowing me to connect. After 5 to 6 hours, if remote desktop connection gets dropsout, I'll exit from vpn and run vpn again and reconnect my work desktop thru Remote desktop connection, it works fine.
At the end of the day, I disconnect from Remote desktop connection and vpn. But But next day when I try to connect my dsktop thru VPN - Remote Desktop Connection, I get following error again.

This conmputer can't connect to the remote computer. Try connecting
again. If the problem continues, contact the owner of the remote computer or
yur network administrator."

So again I'll have to call some body at work place for rebooting, after reboot, it works fine.

Any help or ideas to resolve this issue would be appricated. Thanks in advance.

Thanks
RaviM