The IBM Messages manual has this to say about this error:
2129 (0851) (RC2129): MQRC_ADAPTER_CONN_LOAD_ERROR
On an MQCONN call, the connection handling module could not be loaded, so
the adapter could not link to it. The connection handling module name is:
o CSQBCON for batch applications
o CSQQCONN or CSQQCON2 for IMS applications
This reason code occurs only on z/OS.
Ensure that the correct library concatenation has been specified in the batch
application program execution JCL, and in the queue-manager startup JCL.