Hi Aref.
Can you explain better:
Is the O/S 3.37 in the old PLC, the one you made upload from, and O/S 5.2 in the new PLC, the one you want to dowload the application?
upgrating from O/S should not affect the program in VisiLogic. Only if the O/S in the PLC is lower that the one in VisiLogic it can present problems, but you should update the O/S in the PLC.
Can you please send us an e-mail to support@unitronics.com with the application and a screen shot of the error message you are geting.
regards