I was rolling out some 5505's last week and had some trouble with four sites. The IPsec tunnel went up fine but the network was really slow, take-hours-to-log-on-to-windows-slow.
It turned out the router/modem provided by the ISP ( Telenor ) was the culprit. When I switched to another model the network was just fine.
This one didn't work: Thomson TG585i v7
This one did: Thomson Speedtouch ST546
Thx to Telenor for providing replacement devices on short notice.
If anyone have an insight into why it didn't work - please enlighten me. I don't have the time or expertise to look into it.