Unable to write pattern in VT-Modem-3.

Hi Experts,
I am unable to write a pattern in VT-Modem-3. I have faced an error which says problem encountered while sending string. Error is given below:
SIXNET VT MODEM Wizard
ERROR: Problems encountered while sending Modem Speed String AT+MS=11,1,300,9600
Return Value: AT+MS=11,1,300,9600
ERROR
What should I do now with this?
Thanks in advance.
