The query that is the
Record Source for your main form, generated, I'm guessing, using a Wizard, can not be updated. Since you give no information as to what you're actually trying to do here, it's impossible to give any advice on how you should proceed.
Here is a link to one of the best explanations available as to why queries cannot be updated; perhaps it will be of help to you:
http://allenbrowne.com/ser-61.html