test this registers.Serial= Convert.ToInt32(reader[0]); registers.RegNo= Convert.ToInt32(reader[1]);

While using Convert.ToInt32 you didn't provided the proper value which will convert it to int. So in those two places check properly what value you are passing and whether that value can be convert to int or not. Thanks

registers.Serial= Convert.ToInt32(reader[0]); registers.RegNo= Convert.ToInt32(reader[1]); Not working

https://www.c-sharpcorner.com/forums/radiobutton-and-texbox-value-save-and-delete Can U help in This data

seems reader[0] and reader[1] both or anyone has some invalid data so Convert.ToInt32 method not able to convert to int please check column value in table. Trim if there is any whitespace / null / empty string also verify data insertion is code is proper or not.