MS Word is throwing up 'Error 4608' I haven't a clue what to do.

Hello,

I wonder if anyone can help me here, because I am at a TOTAL los...

I have a Word document that I have been updating for a few years, which is a sort of log. It has worked well up until today. Now, whenever I try to save the updated document, a very old fashioned (looks like Windows 3.1!), error message window appears which is headed 'Visual Basic for Applications' and in the window it says:

Run-time error: '4608': Undefined dialogue record field

There are then four buttons at the bottom labelled Help, Continue (which is greyed out), End and Debug.

I have no idea what this error message means.

Clicking on End gets rid of the error message, but prevents me from saving my updated document, and the next time I try to save it the error message just reappears.

Clicking on Help takes me to a website with the title 'No F1 help match was found', followed by a load of technical computer-geek stuff I don't understand.

Clicking on Debug seems to open a new window, but I do not know what it is... Here is a screen-shot of it:

The highlighted text seems to refer to Bookmarks, which is throws me because I only associate Bookmarks with my web browser, not MS Word. I'm sure I haven't added any bookmarks to my document in any case.

Can anyone enlighten me as to what is going on here please?

Thanks