I cannot figure this one out.

I have a simple macro which adds 40 new worksheets and retrieves data
on each of these new sheets in column C.

Here is where the code fails

Columns("C:C").Value = Columns("D:D").Value

It works for 15 sheets but on the 16th, I get the following error
message:

Run-time error '1004':
Application-defined or object-defined error

Any ideas?