What type of 2000 are you having this problem on? What is the distance from the 2000 to the PMS computer? Have you used the PMS simulator?, did it recreate the problem. On you first post where you monitoring the PMS link at the PBX or at the PMS side. Just wondering wether the RX data is coming from the PBX or from the PMS. The 05 would be ACK and 06 would be for a ENQ the 16 would be a DLE. The DLE message is an indication that the sender of the DLE is requesting the other end to stop. You should get a DLE "<" to get the interface to start again. So you need to identify wether it is the PMS end that is requesting a stop or the PBX end.