Source(s) of Mate Errors?

Hi all,

So in the attached assembly file ("SUBASSEMBLY Back"), I'm simply trying to figure out why the mates folder in the feature manager is lit up, top to bottom, with error messages. Yesterday I had this exact file with no errors, with one mate (...not shown here) suppressed.

Then, when I deleted the suppressed mate, expecting nothing to happen, I immediately got all sorts of errors (...which is the current state of the assembly).

I have two questions:

1.) How could deleting a suppressed mate cause any sort of problems? Shouldn't that have no immediate effect on the assembly?

2.) Any ideas as to what I can do to take care of the errors?

All help is appreciated !

Thanks in advance,

P.S. I can't recall specifically what the mate I deleted was.

SolidworksModeling And Assemblies