Well that's not good.

Of course, it could be worse: at least I understand that I don't understand. Seems that I got confused at

Couple of options:

If you think you know what happened you can try again
You can read the about, frequently asked questions, or users guide to see if that helps
You can post a question at the program blog: platplotter.blogspot.com and mention the context of the error so I can make sure to match up your question with the system logs: Mapserver/get: Bad Plat Id
I read all blog comments before posting, so it may take a while. Also, if you want to send a note but not have it posted just state that in the message.