When the RadGrid is set as initiator in the RadAjaxManager, there is no need to ajaxify the nested controls withing the TemplateColumn, since all controls in the grid will be already ajaxified. Please remove all your AJAX setting for the nested controls and see if it makes any difference.
If the above does not solve the issue, could you please try to set the "EnableAJAX" property of the RadAjaxManager to "false" and see if the error still occurs.
And finally, if both of the approaches does not resolve the problem, please provide the code-behind of your grid or (preferably) open a support ticket with sample, runnable project attached, so we could inspect it locally.
Looking forward to your reply.
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Konstantin, I figured out I needed to have an <itemtemplate> for the sSecondaryProviderNumber column. After I added that All seems to be working as normal again. I will go remove all the controls from the RadAjaxManager as those were just there in an effort to fix the issue. (I didnt originally have those in the page)