[users] incomprehensible error message

[Thomas Steel]

Further to my earlier plea, I should have explained that I get just the same 
error message when I open a previously backed up version of the file, so there 
can't be anything wrong with the file---but somehow in the process. It is quite 
a small file, so the reference to 30,000 columns is nonsense. Does the word 
'sub-document' offer any clue?--it means nothing to me. TS