External Middleware receives RFC error trying to connect SAP

Hello Java & SAP gurus,

There is a JCO middleware (MQ Series) that received an SAP-returned error "RFC_ERROR_SYSTEM_FAILURE", Message: "connection closed without message" (CM_NO_DATA_RECEIVED).

1. Should I see any message in sm21? Or only in dev_rd or dev_rfc?

2. Is this a middleware-JCO error or SAP error?

Unfortunately, when the error occured, RFC trace was not turned on. Will default trace level 1 detect any error?

I looked through all dev_W? logs and dev_rfc? logs and dev_rd but could not find any RFC errors. Does this mean default trace level 1 is not enough to capture such errors?

Does it mean sm21 or st22 can capture the message? I checked st22 but nothing found.

My sm21 log got reset at that time. So, no trace found.

Could you pls help me?

Thanks.

Regards,

Pascal Gabin