Swapped old fx2n for fx3u won't connect.

Hello to all, I recently changed out our fx2n with an fx3u and now unable to connect, I did change the setting in the program with the new plc series # and still no connection to plc, thanks.

Well, someone on another forum said I have an old gx developer software version and that I have to get the 8.45 version to be able to connect with plc, I will try this but still unsure, thanks.