I am experiencing problems after modifying spreadsheets in Excel 2007 (saving
as 2003 compatible .xls format). The files were last sucessfully worked on
in Excel 2003, but may have been created using earlier versions.

PROBLEM: Small files become huge, operations become slow and Excel is pretty
much unworkable.

I have read and tried most of the suggestions in earlier posts, which refer
to checking the last used cell and deleting unused rows and columns and site
information in link: http://www.contextures.on.ca/xlfaqApp.html#Unused.

Although, performing the unused cell deletion, does reduce the file size
marginally (from 6,132KB to 4,432KB), it doesn't solve the problem.

However, if I 'Copy & Paste' the used cell contents and formatting into a
new workbook, this works. File size is reduced to a tiny 146KB.

Does any one have know what could be causing this apparent file corruption,
and a possible fix?