An unconditional rule for the generic identifier 'X' has
already been entered, so no other rules are permitted.
or Previous rules for the generic identifier 'X' have conditions, so the
current one requires one as well.
Compilation continues but no compiled source code file will be saved.
It is an error if more than one element rule can be selected
at any one time and any particular generic identifier can appear in
either only one rule without a condition or several conditional rules.