A configuration line has a maximum length (see MAX_LENGTH_CONFIGLINE at line 30 in src/serverconfig.c). Congratulations, you are the first one to exceed that maximum.
You can split up a line but placing a '\' at the end of the parts. Example:
BanlistMask = deny 127.0.0.1, \
deny 10.0.0.0/8, \
deny 192.168.0.0/16