Hi,
from Microsoft:
http://support.microsoft.com/default.aspx?scid=kb;en-
us;69491&Product=xlw:
SYMPTOMS
When you attempt to inset a cell, row, or column, you
receive the following error message:
Cannot shift nonblank cells off sheet
CAUSE
This error message occurs if the last cell, row, or
column, in your sheet contains data or is formatted. You
receive this error message because the cell or range of
cells will be pushed off the sheet if you insert a new
cell, row, or column.
WORKAROUND
To work around this issue, follow these steps:
Locate the nonblank cell, row, or column that will be
pushed off the sheet.
To determine where the nonblank cells are located, press
CTRL+LEFT ARROW or CTRL+RIGHT ARROW. These key sequences
find the next block of data or the end of a block of
data.
On the Edit menu, point to Clear, and then click All.
Note that this step removes the contents of the cell,
row, or column.
Now you can insert additional cells, rows, or columns.