I am experience a problem when copying worksheets.

I have a workbook with about 9 worksheets. The size of the workbook is
about 1 MB.

When I right click on the last worksheet (named "Smokin Aces"), select "Move
or Copy", select "Create a Copy", and select "OK" it will allow me to make a
copy. When I do this two more times, it still allows me to make copies.
When I try the fourth or fifth time, nothing happens.

When I save the file and then re-open it, I receive an error message:

"Excel found unreadable content in "filename.xls" Do you want to recover
the contents ... "

Any ideas on why this is occurring? I've never had this problem with other
workbooks.

Thanks,
Mike.