Text disappears when format changed in MS Word (Office X)

[James Costello]

I save Word documents in Mac Word 5.1 format while using Office X.
Sometimes when I resave, the format changes to the generic Microsoft
Office document format. After this happens and I open the document,
the text of the document is missing entirely. I an using Panther
10.3.3.

Any ideas?

Thank you.

James Costello