The copybook is same for request and response.The request is parsed correctly but the response is throwing unknown copybook error.
One of the reasons this issue occurred was because the response is 4106 bytes but the copybook only covers 4000 bytes.
A new file called filler.txt was created. This defined a 106 byte filler. Then the mapping file was also changed to pick up this new filler.txt file. Once the filler was added and the mapping file changed to use BFCOMM05.txt and filler.txt for the response, the response was parsed correctly.