MPASM warning #221 = Invalid message number.

The message number specified for displaying or hiding is not a valid
message number.

You either have w = -23 in your header file, or as BigWumpus already
mentioned, you have an old version of MPASM that doesn't recognize
the warning message this entry (w = -230) is trying to disable.

It should look like this;

LIST p = 18F2220, r = dec, w = -311, w = -230, f = inhx32

If that causes an error, then you should update to a newer version of
the MPASM assembler.