Endless save loop in Microsoft Word

It's a Word bug. It sometimes manifests itself when working with formulas and affects versions 2007 and 2010, possibly newer ones too.

To avoid re-typing formulas or saving in compatibility mode (which converts formulas to images):

1. Install a clipboard manager (Ditto Portable is a good one and you don't have to actually install it, it's a self-extracting archive).
2. Switch to Word, press Ctrl+A to select everything and copy it.
3. Use clipboard manager to export clipboard to a file. Clipboard should be preserved anyway, but do it just in case.
4. Close all instances of Word. Copying everything to a new instance will work, but you need a full Word restart first. It may throw some errors when closing the last window, ignore them. Kill it with Task Manager if needed.
5. Open Word and paste your document. If it's not in the clipboard anymore, import it with clipboard manager first.
6. Saving as docx should now work.

Answer from comments in OP:

I retyped all the formulas in a new document, and now it saves without issues.

I finally fixed this by simply following the "Open and Repair" feature in MS Office 2013 (probably in 2010 as well). Check it out - http://support.microsoft.com/kb/893672. This told me my errors (text box and a shape).

Afterwards I put my 2010/13 styles back on while in 2013, saved, and everything took. I hope this helps.

I've just struck a very similar problem --- could save the document in 2003 (.doc) format, but trying to save in .docx resulted in an endless loop of SaveAs dialogs popping up, and no document actually being saved.

The document had pictures but no formulas, and and first I didn't have a clue which parts of the document were corrupted.

If it helps others, I was able to fix the problem by doing the following:

• With an open document, choose Save As.
• Set to save in .docx format.
• [Very important!] Tick the box titled “Maintain Compatibility with Previous Versions of Word”. Word then allowed me to save the document, but indicated it'd fixed some errors. At this point, I could click the Details button for a list of errors which had been fixed.

This enabled me to save a document in Word 2010 format. The document was saved in Compatibility mode, but I could easily revert that by choosing File/Info/Convert to convert it to a full 2010-format document.