[Therion] cs OSGB options

I have had problems with this command if I am not working in areas ST or SN. (Mendip , west part of South Wales.) using cs OSGB:SO # (east part of South Wales) I get error ;- therion 5.3.9 initialization file: C:\Program Files (x86)\Therion/therion.ini reading ... done configuration file: thconfig reading ... done reading source files ... C:\Program Files (x86)\Therion\therion.exe: error -- gelynnen.th [10] -- unknown coordinate system -- OSGB:SO writing xtherion file ... done It runs 100km out if changed to cs OSGBT (read ST) or correctly positioned if using cs EPSG:27700 -calibrate [0 0 0 300000 200000 0] other 100km grids not working but checked, SV SU SS SM SO SP (SD SE NY NZ - Dales) Cheers John S