Sending SMS alerts from IT Assistant

I have a GSM modem connected to my server that is running IT assistant. The following batch file successfully sends an SMS to the number specified as first argument, with message content being specified in the second argument:

echo AT+CMGF=1>com1
echo AT+CMGS="%1" >com1
echo %~2 >com1
copy c:\ctrlz.txt \\.\COM1 /b

The "c:\ctrlz.txt" file contains 026 (Ctrl-Z) binary character which is required by modem to initiate transmission. When I run the batch file from command line, it works fine. However, when I try to define an alert action in IT Assistant that runs this batch file and arguments and test it, nothing happens. CMD terminal window pops up for a split second and then disappears, even if the application launch specified is cmd /k. What am I doing wrong?