I think there may be a critical bit of information missing in the VFX manual ?
Section 14.4 Only one FP package
To replace the floating point pack use:
BUT this does not remove the default NDP floating point recogniser, so any subsequent attempt to use an FP number results in a mysterious crash.
BEFORE doing remove-FP-pack, you must do
' REC-NDPFLOAT FORTH-RECOGNIZER -STACK \ Remove NDP recog