RX problems on iDirect 5000 series

I manage an SCPC net work in Nigeria on NSS 12 satellite with a 3. 8m dish and 2.4m dish at each remote ends.

The iDirect at each end are the INFINITI 5000 SERIES and the BUCs are NJT 5762N C band 10W buc and the LNB is NJS 8477H

But  recently we did  a check on the link which is a back up link (that is, it is not on active tarnsmission at all time ) and we discovered the issue described below.

During  the recent routine site visit, we observed a problem on the link  equipments.

At the remote with the 2.4m dish we discovered  the idirect 5000 modem  has the RX and NET front LED lights yellow/amber and the TX and PWR lights green .
At  the remote with 3.8m  all the lights are green and we could not ping across the remote.

What can be the problem of the link i will need your help here if its a Buc or Lnb problem?

Regards, dapoglobal