can't hide columns

I just started getting an error message that I can't hide columns.

In the Worksheet_Activate() event I have some entire columns being hidden (I:IT). It has worked fine for over a year, and it works fine on other sheets in the same file.
It gives Err number 1004, which is no help. It just says that columns weren't hidden, but doesn't give me any reason for why they weren't hidden.

Are there any typical reasons why the columns can't be hidden?