Worksheet will not scroll

I use Excel 2002 SP3

One of the worksheets in a workbook that comprises several worksheets will
no longer scroll vertically. In other words, when I use the mouse wheel,
slide vertical scroll bar or cursor up and down the sheet with an arrow
button, the sheet view remains static (though the scroll bar moves, the
selected cell appears in the Name box changes and the contents of the cell
are displayed in the formula bar).

Applying a filter still displays the selected rows.

The other worksheets in the workbook are unaffected.

Have I inadvertently altered a sheet property? How can I restore the
scrolling please?

Thanks in anticipation

Howard