Thank you for pointing out how to get info about the Tcl installation (I am a newbee with Tcl!). It turns out I am using an older version (actually I never installed Tcl. My version must come together with Tcl::pTk?!?). With my ecosystem I can create an .exe with PerlApp without problems (beside the speed problem which is not bearable).
I'll try to find out how update Tcl (and make it work together with PerlApp which I fear it will not be easy...). How can you tell Tcl::pTk WHERE to look for Tcl? I can not find any mention of this.