Try this. Open the file in question before opening the assy/drawing. Does it solve now?
The message is "non-matching internal ID". So the FMR part exists, but this FMR is a different file from the original FMR part, thus it has a different internal ID number. (See explanation at bottom of error screen.)
So, if the "new" FMR part is the one you want, click on "Use this file anyway". Then save the assembly.
If you want the original FMR part, do as Steve suggested. But first you should rename the new FMR to something like FMR2. Then find the original FMR part and and open it before you open the assembly. Then save the assembly.
Your suggestion worked, although I had to correct a lot of errors.
The part name was never changed, so I do not know why it would have a different ID number.
Check in your "Dismissed Messages" section in Tools-->Options-->Messages/Errors/Warnings for something having to do with "file not found".
I can't remember exactly the dismissed error message but basically you may have given SW permission by dismissing (and choosing to never show again) an error when you open a drawing, and it cannot find the model file to go ahead and skip it.
It will then display blank boxes in the drawing.
Clear out the dismissed error message so next time you open the drawing it will let you browse for the model.