Did you import that data or something?

Usually this is caused by a ' indicating that it is supposed to be text. In
this case if there is a ' in it but no data you will get what you received.

Try copying a cell from a blank workbook and pasting it in to C20 to see if
you get a different result.

"Dave F" wrote:

LEN(C20) = 0
ISBLANK(C20) = FALSE

How could this be?

This would seem a contradiction in terms.