Thanks for the reply but I have not found a solution to the problem. When I upgraded I used the Telerik installer/upgrader and it also replaced the .dll. In my webconfig there are only short names, ie:
add path="Telerik.Web.UI.SpellCheckHandler.axd" type="Telerik.Web.UI.SpellCheckHandler" verb="*" validate="false" />
add path="Telerik.Web.UI.DialogHandler.aspx" type="Telerik.Web.UI.DialogHandler" verb="*" validate="false" />
However, both version are in GAC but I have never manually dealt with the GAC and if I try to uninstall the previous version of the Telerik controls from GAC it says access denied. Setting the folder/file properties so that it isn't read only doesn't change this.
I'm not sure where to go from here. Any help appreciated. Thanks