RS-232 protocol over USB: dirty characters

Hi All, has anybody experience in writing procedures for DUTs using RS-232 protocol handled over USB (not USBTMC ...) ? I do basically just communicate with them using the PORT command but, even if I set the correct string terminators my proc sometimes work (a little), other doesn't at all .

The problem is always dealing with inputs like a simple

 1.002  PORT         [OTERM LF][TERM LF]
 1.003  PORT         [@COM6]*IDN?

The correct input terminator (DUT -> PC) should be CRLF ; PORT command doesn't allow it with TERM yet but I think this is not the problem.

Have tried with different timeouts, delays, CLR settings etc ... but, no way : the DUT sometimes sends other characters (like ascii 0x05, etc ...) sometimes I just receive 'semaphore related' errors.

As the communication is always good using NI-MAX interactive I/O was wondering if I am missing something in the configuration.

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