Hi thanks for your reply, i have tried it with using the datatype = "system.int32" its thowing an exception "Specified cast is not valid.".
then i used system.string its too throwing a exceptions "system.object does not support".
It seems your column is of string datatype. Thus, you could manually calculate the sum for the column from code-behind. You can refer to the section 'Programmatic solution' under the following document to understand how to manually get the totals for a column in its footer: Totals in grid footers