Oracle Forms

Hi

I have Form 6i menu item code to start an external app using dde.app_begin. The returned id is stored in a global variable for later access. If the user subsequently selects the menu item the code should use the global variable with dde.app_focus to switch to the external app. However I get the error message 'FRM-21011: PL/SQL unhandled exception ORA-106501' which I cant find anywhere. The menu item code is as follows:

DECLARE
AppID PLS_INTEGER;

BEGIN
default_value('0','global.cmid');
if :global.cmid = '0' then
AppID := DDE.App_Begin('extapp.exe',DDE.App_Mode_Normal);
:global.cmid := AppID;
else
AppID := :global.cmid;
dde.App_Focus(AppID);
end if;
END;

Any suggestions?

Thanx