We do something similar. Have you tried issuing:

ON KEY LABEL F2 DO pop_fields WITH VarRead()

and then putting a parameter statement in the top of pop_fields to store the passed value to a variable to use for the check in the case statements? Just a thought.

What we do is:

*--Calling program
ON KEY LABEL F2 DO userhelp WITH program()

*--userhelp.prg
PARAMETERS mprogram

varname = SYS(18)    && current @...GET field variable
paren = AT("(", varname)
IF paren > 0
    subscript = VAL(SUBSTR(varname,paren+1,2))
    varname = LEFT(varname, paren - 1)
ENDIF
varname = LOWER(varname)
DO CASE
CASE varname = "m.letter"
    IF mprogram = "QUOTE"
        DO ("ltrsel.spr") WITH "letter"

*ETC...

>We're still in the process of converting from a FoxDOS system, so I know that makes things a little funny to bein with but there is still a puzzle to me.
>
>We're running in VFP 7.0 but we still have a few data entry screens running with the old says/gets and read cycle. We do the following at the beginning of our code:
>
>on key label F2 do pop_fields
>
>Our pop_fields function evaluates varread() and determines if a popup should be executed on that particular field.
>
>Example:
>case varread() = "STATE"
> do p_popup with ...
>
>If in my pop_fields I say something like:
>
>case varread() = "STATE"
> = messagebox("Hello")
>
>The valid event for STATE is not fired. However, if I actually do my popup routine (which displays a modal form showing a list of valid states) the valid event of the get field is fired.
>
>How does the messagebox supress the valid event and can I cause the same behaviour when I call my popup form?