After migration to macbook pro, excel error "document not saved"

Greetings.

I just bought a new 15" Macbook Pro retina. I migrated from my old 17" 2011 Macbook Pro via wifi. I have been using Microsoft Excel 2011 for a fairly complex spreadsheet (macros, formulas, countif functions, etc. OK, maybe not all that complex). I upgraded because my old 2011 Macbook had gotten way slow.

After migration, my new 15" Macbook Pro is really fast, the display is great. However, with my Excel spreadsheet, I get the "document not saved" error message each and every time I try to save. It simply won't save. I did a LOT of searching, and tried a number of fixes:

1) I used disk utility and repaired permissions. Still won't save.

2) One site recommended upgrading the OS with the latest updates, and also getting the latest updates for Excel 2011. I upgraded the OS to El Capitan 10.11.1, and I got the latest Microsoft Office 2011 (which I believe was from October). Both upgraded/updated. Still with same "document not saved" error.

3) I have always saved this in .xls format (Excel 97-2004 workbook). Some suggested trying to save it to another format such as .xlts, .xlsb, etc. I tried saving in NUMEROUS different formats, and it still gives the error: "document not saved."

4) I have renamed the file to remove any and all unallowed characters (letters only), and still get document not saved.

5) I created simple files, simple names, and the document won't save.

My file and Excel still work on my old, slow but trusty Macbook Pro 2011. I can still work and function with that. However, if I can't use my new computer to do the work I need to do, what is the point of having a new computer? My Excel file is something that I have been using for about ten years, and have added sheets and functionality to it such that it suits my needs very well.

Anyone with any thoughts or ideas would be very welcome. I'm stumped, and I have a sweet new Macbook Pro that isn't much use to me at present. Thanks!