This is an oldish thread, but having experienced a similar problem - receiving a Path/File Access Error and being unable to save my work on several occasions - I accidentally 'fixed' the problem in the following way:
I opened a new workbook in the same instance of excel.
I added enough sheets to the new book to equal the number of worksheets in the error causing book + 1 (i.e. I had 8 sheets in the old book so I created 9)
I deleted the first eight sheets in the new book, leaving me with just "Sheet9"
I copied the old sheets across using the sheets 'Move or Copy' function and pasted them before "Sheet9" (in this way all the sheets retained their sheet numbering so the vba code referencing the sheets was not upset).
I copied the forms over into the new book.
(I had hoped that I could just move all off this back after saving the new book and closing excel, losing my previous work), however, after going through all of this, all of a sudden the error disappeared and I could save my work

- nothing lost!!
Not sure which element in that process sorted things out, but I thought it was worth posting after spending an hour looking for an answer online......