NAT and MLPPP not working correctly

[metalfan]

I have a VERY weird problem. I have this kind of setup on 6 locations, and on two, I have the weirdest problems.

routers: C2610

IOS: 12.0.7T

When contacfting our mail server (SMTP), from a NAT:ed IP, the "conversation" always dies after rcpt to is sent to the mail server. I have setup ACLs and the 'debug ip packet ACL detailed' to see what happens, and I see the packets arriving from the mail server, and also the retransmissions. But somehow, they just dont seem to get thru. Not even if I do a telnet from the C2610, using the NAT:ed IP as the source-interface (telnet mail 25 /source-interface eth0/0). But, as I said, I do se the packets from the debug, so they do arrive anyway. If I do a telnet mail 25 (hence using the outside interface), everything works like a charm.

If I shutdown one of the 2 MLPPP links, everything works like it should with NAT:ed addresses.

As I said, I am running MLPPP w/ 2 links at 6 different location, but on 2 of them, I get this weird problem.

Any suggestions?

[metalfan]

I might ad that I tried upgrading to 12.1.16 , but then no NAT:ed traffic worked at all. At least with 12.0.7T one can surf the web etc, but with 12.1.16, all connections just got resetted all the time (RST sent, I would assume from the router, killing the connection).