When configuring the modem for Call Back Security I receive an error in response to the command AT#SMODEMSETUP.

The modem may have another password already programmed into the modem.
Follow this procedure to set the passwords back to factory default, then reprogram the modem for call back security.
Issue the following AT commands.
NOTE: You MUST use upper case where I do.
AT#RM<enter>.
You MUST shut the modem off within 10 seconds in order for the reset to take place. Now you can setup the modem for call back security.
AT#IMULTI-TECH<enter>
AT#SMODEMSETUP<Enter>
AT#DB2<Enter>

type the letter "y" to continue.

AT#CBN0xxxxxx where xxxxxx is the DB>password. It must be 6 to 10 characters long.

If you wish to have the modem call back a specific number, issue:
ATDTyyyyN0<enter>where yyyy is the number you wish to have the modem call.

If you wish to bypass the call back feature then issue:

AT-DTN0<enter>

If you enter this string, when you get the DB>prompt, you will need to enter the CBN0 password followed by the "-" sign. For example. xxxxxx-

The first passord is now MULTI-TECH and the second is the CBN0 password.