Hi everybody, Thank a lot for your suggestion, but it was more tricky than it looks. Like mention in the first post, there was an error "Invalid attribute value" each time I download the serial configuration. There was no information with this error. Tech support group from RS I've no clue about my problem, but they told me to try the following thing and it worked. -Export the program in .L5K and reimport it in .ACD. So, when I've reimported it, I've received the following warning: Warning: Line 6767: An error occurred while setting attribute TOKENHOLDFACTOR of DF1 DF1 (Value too small.) Complete - 0 error(s), 1 warning(s) It make sense, since this attribute is related to the serial port. Finally, I've download this program (doing nothing for the warning) and now I can change the serial port configuration (online) like I want. Thanks again!