[AccessD] Property Value

I keep getting this message when editing a table definition:

Property Value Too Large

In many cases the table design is questionable, with over 200 fields in
many tables. In addition I have been adding lengthy descriptions to
every column in every table. Until this database I have never before
encountered this message, and have no idea what is causing it. Could be
the number of columns, could be the description length, could be
something I haven't considered. 

The strange thing is that despite this message, my latest changes seem
to save OK.

Does anyone know what is causing this, or how I might investigate it?

Arthur