[users] Incomprehensible error message

[Thomas Steel]

I need urgent help. I have subscribed, but I'm not sure if this is the right 
address to which to send my question. Anyway here goes.
It concerns an Open Document Spreadsheet which I use every day in OO 3.2.
This morning it won't open. I get this error message: "Format error discovered 
in the file in sub-document content.xml at 2,30818 (row,col)."
What on earth does this mean & what can I do?
T.M. Steel