Bizarre Cisco 1841 DNS problem

Hi all, hopefully I'm posting this in the right forum

One of our servers (W2K) internet access stopped working sometime during the last 3 weeks. First I thought it was because DNS wasn't getting replies. I put some ACL rules in the two routers to Permit UDP:domain trafic and log it to the Linux box(network router). I was able to see DNS traffic on my machine (same sub-net) go out and come back. On the server DNS only seemed to go out and not come back.

Well the upshot of all this is that if I turn OFF the logging for the ACL rule, then this one machine suddenly starts getting DNS out and back. No other systems are effected. I don't understand how turning logging on or off should effect anything.

Web traffic doesn't work for this one server either.

The basic configuration is everything goes through a Linux box for routing/firewall, from there into a Cisco 1841 router, down a T1, into another Cisco 1841 router, then to a DSL router.

Any clues? I've read the online help, but it's not helpful enough. Any suggestions would be most welcomed.

Thanks,
Lee