Dynamic NAT table filling up

I have a strange issue with a Bordermanager server. It is 3.9SP1 on a NW
6.5sp7 server. After the server has been running it stops passing traffic to
the Internet. I checked the NAT table and it has 5000 entries (the max I
believe) The entries are old, so it looks like it is not refreshing the
table.

If I disable NAT on the public interafce, then enable it things start moving
again.

Any ideas?

Thanks,

Jim