Chris, It's hard to say without seeing the code in action. Try putting a break on the line where $.blockUI is called. Based on your description it would seem like $StoreUpdateForm[0] is null at that point.
Mike > success: function(data) { > $StoreUpdateForm.empty().append(data); > $("#CloseBtnID").bind("click",function(){ > $.unblockUI(); > }); > $("#SaveBtnID").bind("click",function(){ > alert("coming soon"); > }); > $.blockUI($StoreUpdateForm[0],{padding:'2px', > borderColor:'#3F6F5E', top:'25%', left:'50%' });