Hi Abdullah,
1st check loop test and verify the connection b/w transcoder and a specific TS in BTS.In order to perform test TS must be in state COM(block).
After blocking TS initiate Loop test by following command.
RXLTI:MO=RXOTS-TG#-TRX#-TS#;
Mostly it happen when Abis E1 TS mismatch if VSAT media is using otherwise check TRC links may be fluctuating or Down.