Hi, thank you for contacting JustAnswer.com. My name is Russell. I will do my best to provide the right answer to your question.
Though there is little information available for Becker map devices, I suspect that you simply applied to your Active 5, an update or a map meant for another Becker device, that has an 800 pixel by 480 pixel screen, which your Active 5 lacks.
This would make it impossible for the update, or the map, to display on your Active 5, leading to the error message you have mentioned, about "can't accept 800x480".
If this doesn't sound right, in any way, or if you need further advice, please let me know, and I will continue to advise you as appropriate, and to help you with this problem if I can (and if I cannot help, to turn this problem over to other Experts here.)