"Unknown Field" Problem

I am editing our store's invoice / inventory Access database, originally written by a friend of our family as a school project. It works, but not perfectly, and that is why I am trying to improve it. What I am trying to do exactly is add a series of checkboxes (e.g. "carpet", "laminate", etc.) to indicate whether or not the customer's invoice included those items, so I can make a macro for word to automatically print customized thank-you letters. I copied and pasted some of his working, pre-existing check-boxes, set up fields in the related table, and modified the control source of the check-boxes to those fields, yet I still get an obnoxious "Control can't be edited; it's bound to unknown field "Cpt"", etc. Looking at the table, my columns appear the same as his, yet mine do not work. I even went into code view and copied and pasted the code for his checkboxes, changing them as appropriate, yet it still does not work. Any help would be very welcome.