I got problems with too many different versions of prototype and scriptaculous.
While I already used features in my own code that used a certain prototype
version I replaced the version of your code with prototype 1.5.1. That version
does not work together with scriptaculous 1.7.0. Therefore I got 1.6.0_rc0 and
scriptaculous 1.8.0pre, now everything works fine again...
I got problems with too many different versions of prototype and scriptaculous. While I already used features in my own code that used a certain prototype version I replaced the version of your code with prototype 1.5.1. That version does not work together with scriptaculous 1.7.0. Therefore I got 1.6.0_rc0 and scriptaculous 1.8.0pre, now everything works fine again...