Unable to insert a new row in Excel 2007

Excel thinks you have data in all the rows in your workbook.  If you do what the message says and press ctrl-End, you will probably find yourself on the last row.  This can happen for various reasons - you might actually have a value on the last line, or Excel might not have readjusted its used range properly, which can be caused by formatting.  In either case, select all the rows from the real end of your data to the bottom of the workbook, and delete them - don't Clear the contents, actually delete the rows by right clicking and selecting Delete.

This should give you space to insert rows.

Where I have said 'workbook' above I obviously mean 'worksheet' - brain not working too well this afternoon, I fear