Pelleg,
The reset command is
"Bu cdr pri/sec" & than "rel cdr pri".
Also, you can try "bu po (portno.)" if the CDR is running thru a data extension.
Did you checked the response of
command: " Test CDR Pri" or "test cdr pri lo"
the error test 215 & 213 both should pass if the communication between the swtich & the PC's Com Port where the SMDR software is running is OK.
If the test 215 fails, Check the cable, the connections & the Com port of PC, all these should be OK, Also if you are using the system port(EIA) as the CDR output port check for the connectivity of serial cable as well.
If the test 213 is failing & 215 is failing, just try removing the CDR config from " ch sys CDR" & putting it back In. This should resolve your problem.
Best of Luck, & share the result.