The above modem does not support the AT^SSMSS (Set Short Message Storage Sequence) command. In the RcWare command definition file for the respective modem (usually the Siemens MC35i is selected), this command is on the last line.
It is necessary to delete it:
Settings - Computer resources - Modem - (select modem type in AT modem initialization commands) - Edit AT - (delete last line) - Save AT - OK - OK - restart RcWare.
The port monitor also helps with diagnostics, in which we can monitor all communication between RcWare and the modem. The port monitor is activated and deactivated by Ctrl-M - be careful, it only works with the licensed program!