router problem

Hi I am facing a problem with my 1720 router

My remote router pings till i open a web site. the moment i open a web site on my far it stops pinging.

There are lot of input and CRC errors in sh int s0 output.

i connected both the router with help of CSU/DSU (Modems) one in master

mode and one in slave mode but problem still continued. Media was totally by passed. Any one can tell me where is the fault in the router

or modems. Router is WIC 2 AS smart serial. Modem type is Multitech AM

Please advise on priority.