Input string was not in a correct format.Couldn't store in Item_type_code Column. Expected type is Int64."
Based on the error, Item_type_code is expected to be of type Int64. But, you are passing string:
dr(2) = Convert.ToString(txtItemType.Text)
Check the database design. Based on the datatype expected, pass on the value accordingly.
For now, based on error, following should resolve:
dr(2) = Convert.ToInt64(txtItemType.Text)
But, make sure the value has to be of Int64 type.