Indeed, as Pricy suggested it is best to upgrade to teh latest build of RadControls. However, before you upgrade you can test whether the following script fixes the issue:
//Append tooltip to end of document
form = document.forms;
Pleas,e insert this script under the ScriptManager declaration and test whether this fixes the problem. If so, remove the script and upgrade to the latest version and everything will work OK.
Note, that keepoing the script along with your current version instead of upgrading is not recommended and could cause later problems - I provided it only for test purposes and the real solution is the suggested upgrade.
the Telerik team