ModalPopupExtender + ScriptManager

Hi,

I have a custom control which uses ScriptManager to call various JavaScript functions.

I have a situation where I have an aspx page with an instance of my custom control and all the functions execute correctly.

I also have an instance of my custom control on a ajax:ModalPopupExtender. None of my JavaScript functions will execute except for the "built-in" functions such as 

window.onload

or ones that are triggered from client-side attributes such as

e.Row.Attributes("onkeydown") = "return ProcessKeyDown(event, '" & sEdit & "');"

Any other JavaScript function executed from code such as

ScriptManager.RegisterStartupScript(Me, Me.GetType, "ShowAlert", "ShowAlert('Why wont this work?');", True)

doesn't work.

Hoping someone has some ideas?