Google is your friend... a search for that phrase will get lots of hits, and
support.microsoft.com has a good knowledgebase for this stuff...
From microsoft:
http://support.microsoft.com/default.aspx?scid=kb;EN-US;q170081
CAUSE
This problem occurs if both of the following conditions are true: . You
create a cell comment in any cell in a column.
-and-
. You try to hide the column to the left of the column with the cell
comment, the column with the cell comment, and all the columns to the right
of the column with the cell comment.
For example, this problem occurs if you place a cell comment in cell IR1,
and then try to hide columns IQ:IV (at one time).
NOTE: Depending on the location of the column that contains the cell
comment, you receive the error if you try to hide the column with the cell
comment and all the columns to the right of the column with the cell
comment.