Strange "ERROR was returned on AT command: ..." error

Hi Tomas.
Sorry for bothering you again.
One of our customers have faced to the following error, returned by Boomerang library:
ERROR was returned on AT command: AT+CMGS=125>0001000C9145114644662500F17FCDF27C1E3E974166F9BB0D42BEE7F4E6DB9DA6BFE52014FA3DA783C6E8B0FB5C2683E6F430BD3E4F2914D4F29C0E028174A0B05C3C0FCFDBE53C794E86C514537A985E9FEB40CE3728EC9EDFCB7205314C2F83403AD0EC757BC960B01B28A6A3C574B51C08DA5448CB70761EA4032900

I suppose, here should be an extended error description, not just "Error", isn't it? I found in the code the constant: errsErrorReplyOnATCommand = '%s%s was returned on AT command: %s';
So, how can I get the real error description?

Backgrounds: The customer has the Motorolla G20 GSM modem and it works strange. Sometimes it sends SMS properly, sometimes shows the foregoing error, sometimes show "No reply on AT command: AT+CMGS=125>0xxcxcxcxcxc...." error.
How can I get rid of these annoying errors?
Customer uses 19200 baudrate and Motorolla T260 equipment type.

Any help is greatly appreciated.

Thank you.