>Specify an include file for the form that has READONLY defined
>as a compile-time constant. eg #DEFINE READONLY -1

You can hose yourself in plenty of different ways by being careless about the names that you give Compile time constants. Any time you create a constant with the same name as a VFP keyword, oyu run the risk of your constant value being used instead of the keyword when your code is compiled.

Lesson? DON'T USE VFP KEYWORDS as CONSTANTS. (or variables for that matter).