Unfortunately, it did not help. When I work at my home office on CS5/mac os 10.6.6/intel chip, I get no error. At my day office G4/10.4.11/CS3 I uninstalled and re-installed Form Toolkit/deleted cache/restarted Dreamweaver, re-activated Form Toolkit. When I try to modify the Show If behavior that was applied at home, I still get the following error when I try to exit from the Toolkit Show If dialog:
I also get it when I delete the behavior and try to re-apply it.