GridView Pagie navigation gives Error randomly

Question

Hi,
I am facing an issue in GridView Paging. with source code locally it's working fine. when i deployed it on server some times its giving after 4 times, sometimes after 8 times, after 10 times like that.
when ever User search the data, istored that DataTable data in ViewState for paging and sorting purposes.
I strucked here. plz help to sort out the issue. it's urgent. project is in UAT phase.
find the attached code having both aspx and aspx.vb file. bold and Red colour code is used for Page navigation.
kindly check and help... 
 
Regards,
Venkat