The way canned GridViewCommandColumn buttons are specified in web forms has changed between version 13.1.9.0 and 15.1.4.0 of DevExpress.

<dx:GridViewCommandColumn Width="150px">
   <ClearFilterButton Visible="true">
   </ClearFilterButton>
   <EditButton Visible="true">
   </EditButton>
   <NewButton Visible="true">
   </NewButton>
   <DeleteButton Visible="true">
   </DeleteButton>
</dx:GridViewCommandColumn>

 
 

...now becomes one long, single line of markup like so...

<dx:GridViewCommandColumn Width="150px" ShowClearFilterButton="True"
      ShowEditButton="True" ShowNewButton="True" ShowDeleteButton="True" />

 
 

The old markup will cause an error so you have you make the change.