P2P Queueing causing VPN trouble....

I set up P2P queueing per Cibernet’s example in the following post:

http://forum.mikrotik.com/t/gamers-are-complaining/5124/1

This seemed to work great. However, after I enabled the simple queue, the customers on my network that have offices uptown and downtown connected via a VPN with SonicWall routers could NO longer establish VPN tunnels. As soon as I disabled the queueing for P2P the VPN’s come back online.

What would cause this?

Thanks!