parallel processing -> CALL_FUNCTION_SEND_ERROR

hi gurus,

i have implemented parallel rfc call in my main rfc-function module ( FuBa_1 ).

The main rfc-function module gets up to 250 data sets in 1 request.

These data sets are processed by another function module( FuBa_2 ). in parallel with the restriction that max. 3 parallel calls at once are allowed.

The FuBa_1 gets the request 3 times in 4 minutes.

There was requirement that this FuBa_1 cannot run longer then 20 seconds.

I have implemeted a timeout.

The run of the FuBa_1 is terminated when

1. all results of parallel processing has been received ( number of sent tasks EQ number of received tasks )

2. timeout has been reached

the problem is that 1 or 2 times in hour comes the short dump CALL_FUNCTION_SEND_ERROR

An error occurred when executing a Remote Function Call.

"CPIC-CALL: 'ThCMSEND' : cmRc=18 thRc=0#Statistik nicht aktiv "

Status of connection.... "CODE=CM_DEALLOCATED_NORMAL CM_SEND_RECEIVED

CM_COMPLETE_DATA_RECEIVED SAPCODE=0 CONV=49357134"

Internal error code.... "RFC_IO5"

There is an error in the communication system. To clarify

and resolve the error, contact your system administrator.

FuBa_1 and FuBa_2 are in the same SAP system.

Any idea what can be the cause of this short dump?

thank you!

regards,

michal