CustomAttribute in Mobile controls

[JL]

I have a js file with the function SelectedIndexChanged

I have added the below code also in the aspx
<script language="javascript" src="/Scripts/Search.js"></script>

In the cs file I have added the customeAttribute as shown below
ddlSrch.CustomAttributes.Add("onchange", string.Format(
"SelectedIndexChanged('{0}','{1}','{2}');", ddlSrch.ClientID,
tbSrch.ClientID, tb1st.ClientID));

In the web.config I have enabled
<mobileControls allowCustomAttributes="true" />
But still the javascript method is not called.