>>Nicola,
>>Don't know, but have you tried
>>

>>SET CLASSLIB TO MYTEXTBOX.VCX IN MAIN.EXE  ADDITIVE
>>

>
>Sure.
>In the init sequence of my application, I launch a method setClasses() that does exactly this.
>
>Moreover, to call an external form (the one included in CHILD.EXE, just to be clear), I use a procedure DoForm() contained in MYLIBRARY.PRG (this PRG is built in the MAIN.EXE).
>This procedure instantiates an object (oModule) contained in a common class MODULE stored in MODULE.VCX (included in every project).
>Once created oModule, I fire the method oModule.doForm(myformname).
>All this, just to say that even repeating the set class at this time, the error persists.
>
>Nicola

It works for me.
Just make sure you pass the fullpath to Your Main.EXE:

SET CLASSLIB TO MYTEXTBOX.VCX IN C:\whatever\MAIN.EXE ADDITIVE