OK. Let me tell you step by step what I did.

1) Downloaded the AJAX toolkit and modified the sControlContactAddressUpdate.htm as follows
1.Changed the sforceclient.js file location to https://www.sforce.com/......
2.Since I am accessing the scontrol from within salesforce, changed the pageinit function as follows:

function pageInit() {
contactHeader = document.getElementById("contactTable").firstChild.innerHTML;
sforceClient.init("{!API_Session_ID}", "{!API_Partner_Server_URL_60}");
loadAccountInfo();
setupForm();
}

I want users to modify the contact addresses only for the account for which they click the custom link from. So, I took out the functions (two of them) and html code that populates and manages the drop downs and the DIV.

Everything else is unchanged.

The way I figured that the account ID is getting lost for some account is, if I put an alert to show account ID before I call the sforceclient.js, I can see the account ID and if I put the alert afterwards, I don't even see an empty alert. I think it generates 'Object expected' error in sforceclient.js, I believe.

There are two things I don't understand (1) if I hardcode my username and password in htm file where it requires and then open it in browser, it works perfectly (2)If I make it a s-control and then open it from within salesforce, it works for half of the accounts and doesn't work for the other half. It works for sforce account but doesn't work for U of Arizona account for me.