Further to that.
I created a new radTextBox on the form, focus does work on the new one.
However, the first control that failed is on a div who is defined as:
<div runat="server" id="pnlMovement" style=" background: #E0E0FF;
position: absolute; width: 99%; height: 30px; left: 1px; top: 500px; z-index: 10;
border-color: Navy; border-style: solid; border-width: thin;">
What I do is I hide and reposition this div as needed.
The error happens to any RadTextBox on this div and not to any RadTextBox not on the div, therefore it appears that the div is the issue.
After even further study. The issue seems to be the postback. After a postback it happens.
Also please note that I am using a RadAjaxPanel for the entire form.