have some big Excel spreadsheets, 50 columns by 65525 rows (but
definitely not 65536), 45MByte. They are all very similar, just a few
formala tweaks different

On one of them, the top nine rows have become "invisible"

It is possible to navigate through all the cells involved with the
cursor keys- the formula bar. name box bar etc all function correctly
and show cell contents etc. They are just not visible
The missing rows are not hidden
The missing rows are not filtered
The missing rows have a standard row height
The missing rows are not locked

If I move the cursor from row 10 towards the top of the sheet, its
shape changes to a bulky solid cross, the same cursor one gets when
one is outside the range (it wouldn't do this if the rows were hidden
or short??)

I can Select All, Copy and Paste to a brand new workbook and the
missing rows will appear. If I Select All on THAT workbook, Copy and
Paste back to the original workbook, they go AWOL again.

I have googled on this problem and can't seem to find the right
keywords to track down whether any body else has reported it. There
were various hints for similar problems, invovlving tricky mouse
manipulation (as above), but these don't work in my case.

I have had this problem before with other smaller spreadsheets and the
only solution has been to recreate the spreadsheet by pasting into a
brand new one. This I am reluctant to do with a 45MByte workbook.

Any suggestions?

Geoff Lambert