Hi,
I have an application using the Beta2 and I'm facing some Script runtime exceptions.
I found that when I was accessing pages with Ajax components, an exception message was launched, but only if a hover menu (not AJAX, just the menu component) was extended.

 I debugged with the nStuff.WebDevHelper, and here's the exception's details:

Microsoft JScript runtime error
Sys.ArgumentUndefinedException: Value cannot be undefined.
Parameter name: element

Script Error Location and Callstack:

at http://localhost:1100/MOBILITE/ScriptResource.axd?d=wRE6wK03dsI33pyG-6FJR2790fAaa1F6xWAgG5fse6dDtDK_ffIDNmrpLVEAy6b-rbwKNnSmBQMb3rIOckaOM0gxYmZhssmqUn8pDrwI4_OEpjUIegAYqSO9R9zYM9Q10&t=632980773940000000 [11151]
    Sys$UI$DomElement$getVisible
    code: throw e
at http://localhost:1100/MOBILITE/ScriptResource.axd?d=i6dyljVcuio-QbyRNVcP8W1Bfxqt95ACt1dyzV-LhZT1BvOaG3M54mnLN9W4rPRb3YpFv8TK1kNU8WVmRVP8HNO1ZrUAmEwsz9-NmMNqizE1&t=632981583600000000 [275]
    JScript anonymous function
    code: if (Sys.UI.DomElement.getVisible(elt))
at http://localhost:1100/MOBILITE/ScriptResource.axd?d=hKDPCfCD7LH9bOibxqvE0Wyr6YBdyrgUq2k2Rfb3ojl34-oyF13zLSh8tJSRKZ1fjNF3-udWoD4KD1Kxe54jkd1XC_BqjsedyQZ_hN8Ktbe-qbP4RokgfIyu4iVDd-cst2mtKAPAIVxIlVFw4WZ6W6B1YcLEtCYv1SrjWAZjEqk1&t=632987568711619605 [2949]
    Sys$_Application$dispose
    code: disposableObjects[i].dispose()
at http://localhost:1100/MOBILITE/ScriptResource.axd?d=hKDPCfCD7LH9bOibxqvE0Wyr6YBdyrgUq2k2Rfb3ojl34-oyF13zLSh8tJSRKZ1fjNF3-udWoD4KD1Kxe54jkd1XC_BqjsedyQZ_hN8Ktbe-qbP4RokgfIyu4iVDd-cst2mtKAPAIVxIlVFw4WZ6W6B1YcLEtCYv1SrjWAZjEqk1&t=632987568711619605 [3138]
    Sys$_Application$_unloadHandler
    code: this.dispose()
at http://localhost:1100/MOBILITE/ScriptResource.axd?d=hKDPCfCD7LH9bOibxqvE0Wyr6YBdyrgUq2k2Rfb3ojl34-oyF13zLSh8tJSRKZ1fjNF3-udWoD4KD1Kxe54jkd1XC_BqjsedyQZ_hN8Ktbe-qbP4RokgfIyu4iVDd-cst2mtKAPAIVxIlVFw4WZ6W6B1YcLEtCYv1SrjWAZjEqk1&t=632987568711619605 [49]
    JScript anonymous function
    code: return method.apply(instance, arguments)
at http://localhost:1100/MOBILITE/ScriptResource.axd?d=hKDPCfCD7LH9bOibxqvE0Wyr6YBdyrgUq2k2Rfb3ojl34-oyF13zLSh8tJSRKZ1fjNF3-udWoD4KD1Kxe54jkd1XC_BqjsedyQZ_hN8Ktbe-qbP4RokgfIyu4iVDd-cst2mtKAPAIVxIlVFw4WZ6W6B1YcLEtCYv1SrjWAZjEqk1&t=632987568711619605 [2318]
    handler$_browserHandler
    code: handler.call(element, new Sys.UI.DomEvent(window.event))

* And the line which is finding the null parameter is in the 'PreviewScript.js', when calling the folliwong statement:
                  Sys.UI.DomElement.getVisible = function Sys$UI$DomElement$getVisible(element)

If someone has a clue about how to rosolve it ????
I'd appreacite a lot your help

I'm getting a similar JScript message any time I try and use any of the AJAX controls.

 On this line:

This error: 

Microsoft JScript runtime error: 'Sys' is undefined

 Not even sure where this is coming from. Any further help is appreciated.