Hello everyone!

I have a problem, and while I do have backup files (a week old), I cannot think of any reasonable explanation for what is happening.

Last night a co-worker was working on a Shared File, was doing some text inputs (adding dates & notes) and some format changes (highlighting certain cells). They saved and closed out the file (in .xlsx format as it has always been) using Excel version (12.0.6504.5001) SP1 MSO (12.0.6320.5000).

This morning, when the tracker was being opened, an error displayed as follows:
"Excel found unreadable content in 'filename.xlsx'. Do you want to recover teh contents of this workbook? If you trust the source of this workbook, click Yes. (Yes) (No)"
I hit Ctrl-Shift-i to get the code for the error (101648)

Clicking no the first time and making a copy of the file, then click Yes. Yet another error is displayed as follows:
"Excel cannot open the file 'filename.xlsx' because the file format or file extension is not valid. Verify that the file has not been corrupted and that the file extension matches the format of the file. (OK)"
I hit Ctrl-Shift-i to get the code for that error (101590)

I then tried to open a new workbook and link it to certain cells, but it morphs my formula and returns a #REF error

The original formula I type in is:

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The formula that I see after I hit enter is:

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Which is just odd in and of itself, so then I started browsing google to see if anyone else had encountered such an issue, and while I could find responses on the errors alone, I couldn't find anything that matched what was happening to me.

I also tried to rename the file to .xls and .xlsb and tried to open the file. As well as using Excel 2003 with the converter to open the file.

So far everything I have tried has failed to work.

Has anyone seen anything like this? Have any thoughts on solutions?

Your help is greatly appreciated!

Thank You,
John