external references that should be internal

I update files monthly and save them each month with a new name (eg. Jan, Feb, etc.).

In the file I have a reference from one tab to another tab within the same file. So every time I re-save this file with a new name, it should still reference the cell in the other tab - same file.

BUT on 2 occasions this reference changed to an "external" reference to the previous month's file.

I've been doing this every month for over 2 years and this problem has only happened 2 times. I know others that have experienced this, but nobody knows what caused it.

Does anyone know what would cause this? The biggest problem is that I may not notice this has happened for a long time.

One other thing I might add. I use an older version of Excel (2000). I share these files with other people who may have newer versions (I'm not sure who has what). Can sharing these files with others over a network system have something to do with this? Can opening "read only" when someone else is in the file and then saving as a copy do this?

It lists only the external references. Is there something specific I should be looking for when the dialog box opens?

Thanks
marnie

Thanks Oldchippy,

I know how to find all my external links, what I'm trying to figure out is how internal links can spontaneously become external pointing to another file after 2 years.

Here's what the internal link looked like for 2 years

=+Input!N39+Input!AP39

Every month I'd update the file with new data and this reference would pick up the updated data just like it should.

Then after 2 years the formula suddenly changed to this

=+'T:\FY07\October\[oct final.xls]Input'!N39+'T:\FY07\October\[oct final.xls]Input'!AP39

Since I never go back and revise older month's, this October file would never get updated. So when I tried updating for November data, it was still picking up October's. It appeared to only happen in 1 tab, 1 column, but multiple cells just like this.

The rest of the file maintained all internal and external references as I put them in.

This scenario only happened to me once before. And now I find out, it's happened to others in my office and nobody knows what causes it.

It worries me because I can't be constantly checking to see if I have more external references than I intended.

Thanks again for your attention