why are my customactions not working anymore?

[xsintill]

Can't get CustomAction to work with script. I tried different scripts and now i simplified it to a simple messagebox but still the installation breaks and goes to the setup unsuccesful screen. strange thing is i have a customaction working but that is the setup.rul.

this exported function i have linked to a customaction and it is sequenced in the installation execution section after installfiles with deferred execution and synchronous(ignores exit code) return processing
what might i be doing wrong

export prototype MB();


function MB()
begin   
	MessageBox("Test",INFORMATION);
end;

[xsintill]

I had above code in a seperate script file. by moving it to the setup.rul script i could get it to work.Don't understand why .