Hello Gustavo,
a couple of things: firs of all, you do not use any authentication, is that right ? What is this router connecting to, an ISP ?
Regarding the input errors: try to put the command ´ip mtu 1452´ or ´ip tcp adjust-mss 1452´ on the ATM0.1 subinterface as well. You could also try and change the ´dsl operating-mode´ to ´ansi-dmt´, check if that makes a difference...if not please post back and we´ll look further.
Regards,
Nethelper