I'm using the latest version of ECL (which is 0.9j). The apropos example works fine, but I'm having the same problem in lispworks (personal version 5.0) I've tried sending an array back (suing list-to-rdnzl-array) instead of a string, but pretty much the same thing happens.
I've taken Iver's suggest and re-written my program to have the .net code call the callback which set the edit-box's value from within lisp, which does work. I initial tried to mimic the apropos example and use an EventHandler instead of using my callback, but for some reason, RDNZL couldn't find the EventHanlder type when I tried to import it from the System namespace.
Thank you for your help with this problem.