The only thing I see wrong is the skip1 in-between NS and LONG. Should have a space in there. But that won't cause the described error.

It does compile without error if I create all the variables and fix the skip.
Code:
TIME  var BYTE[11]
WARN  var BYTE
LAT   var BYTE[10]
NS    var BYTE
LONG  var BYTE[11]
EW    var BYTE
SPD   var BYTE[6]
DIR   var BYTE[6]
DATE  var BYTE[6]

SERIN2 PORTB.1, 188, 3000, RXERROR, [WAIT ("GPRMC"), skip 1, STR TIME\11\",", STR WARN\1, skip 1, STR LAT\10\",", STR NS\1, skip 1, STR LONG\11\",", STR EW\1, skip 1, STR SPD\6\",", STR DIR\6\",", STR DATE\6]

RXERROR:
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