Try removing the single quote around the
amt
variable:
select voucher_date as VCDate,voucher_code as VoucherNo,receiver_name as PartyName,expense_head_name as Purpose,voucher_amount as Amount from payment_voucher where voucher_code='" + txt_vc_number.Text + "' or receiver_name Like '" + txt_party_name.Text + "' or voucher_amount=" + amt + "