Macro error-"Selection is too large"
 

I have a macro that counts the rows of a set of data. It then copies one row
of formulas and pastes them to new columns to the right of the existing
data...using "numrows" to determine the paste range. Usually, this works
fine, but occasionally, I get an error message of "Run-time error '1004':
Selection is too large".

The most recent instance of this was a file with 18515 rows of data. I have
had larger files that ran with no problem. Any idea what is wrong here?
--
CG