Auto Fill numbers - wrong values

Dear all,

I have a large spreadsheet in which I need a column with numbers 1, 2, 3, 4, 5 etc. But with this existing spreadsheet, when I fill in 1, 2, 3, 4, 5, and then drag to auto fill down 5 more cells, I end up with 10 cells of 1, 1, 1, 1, 1, 1, 1, etc. I will need to insert / delete rows in this spreadsheet and update the numbers, so manually number is not an option.

When I drag and drop with right click, only the "Copy Cells" function is available, everything else is grey and not clickable. In Options --> Advanced, the drag and drop option is checked.

When I go to a brand new Excel file, I have no problems auto filling, and all options are available (Fill series, fill formatting only, fill without formatting... )

Thank you for your help.

Thank you Sixthsense.
Sorry all, I just found the answer. Can't auto fill series when the filter is on even if the cells are adjacent cells. Can do it once I clear filter.