Most likely cause of network input errors?

He believes it is a case of the LTMs not understanding some type of traffic coming across the port and dropping it as a result.

isn't it input drop rather than input error?

errs in/out - This counter reports the total number of frames with framing or CRC errors 
drop in/out - This counter reports the total numbers of packets dropped due to unknown L2 protocols or VLAN IDs (unrecognized packets), or because buffers were exhausted 

sol9932: Interpreting the counters displayed by the bigpipe interface command or the bigpipe trunk command