I have been wondering for some time why the fill series functionality is
sometime not available. When you right-click on the fill handle and drag it
to fill adjacent cells, the series option is grayed out in the menu and there
is no way to get Excel to do anything other than copying cell values.

I searched the Web and couldn't find an answer, so I decided to share my
findings.

I know for shure adding auto-filters to a spreadsheet deactivates the fill
series functionality. If you are aware of any other reasons why it may be
deactivated, please share it here.

BTW, here is my workaround to the problem, I simply create a new workbook,
create the series I want, and then copy and paste it in the original
worksheet.

Hope it helps.