>>Try:
>>

>>oMyVCXClassinMainEXE = NEWOBJECT([ClassName],[ClassVCX.VCX],full_path+[Main.EXE])
>>

>
>Thank you Borislav,
>but I think that this would not help.
>
>Infact, I create objects stored in classes compiled in the MAIN.EXE without problems.
>
>Is when I try to launch a form compiled in the CHILD.EXE that uses classes stored in the MAIN.EXE that I got the infamous "ERROR INSTANTIATING CLASS" error.
>
>Example:
>The MAIN.EXE includes a MYTEXTBOX.VCX class.
>The MYTEXTBOX.VCX class includes a class named TEXTBOX_EMAIL.
>
>I use this class in many cases and therefore in many forms.
>
>AT DESIGN TIME, in a form contained in the CHILD.EXE, I add a TEXTBOX_EMAIL control.
>
>The MYTEXTBOX.VCX in included in the MAIN.EXE and excluded in the CHILD.EXE
>
>This situation fires an error.
>
>Nicola

Nicola,

Don't know, but have you tried

SET CLASSLIB TO MYTEXTBOX.VCX IN MAIN.EXE  ADDITIVE