Excuse me, what is the reason for this error?
Literally, GAUSS is telling you that your code is trying to use
delcols, but your GAUSS installation does not know what
delcols is a GAUSS procedure that removes specified columns from a matrix. This procedure was added to GAUSS in version 18 or 19, I believe.
Most likely this error is occurring because you are using an older version of GAUSS to run code which requires a newer version.