c# - Application stops when SQL Server CE command executed -

when debug program works fine until gets to:

sqlcecommand mycommand = new sqlcecommand("insert dbo.login values ('" + usernamebox.text + "','admin', '" + saltedcryps + "', '" + hashedresult + "')", myconnection);                     mycommand.executenonquery();                     messagebox.show("thanks registering!");                     this.close(); 

then stops, closes form , other forms except mdi form. can help?

here code:

using system; using system.collections.generic; using system.componentmodel; using system.data; using system.drawing; using system.linq; using system.text; using system.threading.tasks; using system.windows.forms; using system.security.cryptography; using system.data.sqlserverce;  namespace event_control {  public partial class registerscreen : form {     public registerscreen()     {         initializecomponent();     }      public static string a;      private void registerscreen_load(object sender, eventargs e)     {     }      private void cancelbutton_click(object sender, eventargs e)     {         this.close();     }      public string radiobuttons()     {         if (userbutton.checked)         {             return "user";         }         else if (adminbutton.checked)         {             return "admin";         }         else         {             messagebox.show("you must select account type");             return "error";         }     }      private bool checkifusernameexists()     {         sqlceconnection myconnection = new sqlceconnection("data source=eventcontrol.sdf");          try         {             myconnection.open();         }         catch (exception ex)         {             messagebox.show(ex.tostring());         }         string checkuser = "select * login name = '" + usernamebox.text + "' ";          sqlcecommand checkuser = new sqlcecommand(checkuser, myconnection);          if (checkuser.executescalar() != null)         {             messagebox.show("username exists");             return false;         }         else         {             return true;         }     }      private bool checkpasswordsmatch()     {         if (!passwordbox.text.equals(confirmpasswordbox.text))         {             messagebox.show("sorry, passwords not match, try again", "password error");             passwordbox.text = "";             confirmpasswordbox.text = "";             return false;         }         else             return true;     }      private bool checkusernameempty()     {         if (usernamebox.text == "")         {             messagebox.show("enter username");             return false;         }         else             return true;     }      private bool checkpasswordsnotempty()     {         if (passwordbox.text == "")         {             messagebox.show("password box empty");             return false;         }         else             return true;     }      private string saltpassword(int size)     {         rngcryptoserviceprovider crypto = new rngcryptoserviceprovider();         byte[] buff = new byte[size];         crypto.getbytes(buff);         return convert.tobase64string(buff);     }      private string hashpassandsalt(string passwithsalt)     {         hashalgorithm hashalg = new sha256cryptoserviceprovider();         byte[] bytvalue = system.text.encoding.utf8.getbytes(passwithsalt);         byte[] bythash = hashalg.computehash(bytvalue);         string base64 = convert.tobase64string(bythash);         return base64;     }      private void registerbutton_click(object sender, eventargs e)     {         = radiobuttons();         string saltedcryps = saltpassword(10);         string passwithsalt = (passwordbox.text + saltedcryps);         string hashedresult = hashpassandsalt(passwithsalt);          if (a == "admin")             if (checkusernameempty() && checkifusernameexists() && checkpasswordsnotempty() && checkpasswordsmatch())             {                  {                      sqlceconnection myconnection = new sqlceconnection("data source=eventcontrol.sdf");                     try                     {                         myconnection.open();                     }                     catch (exception ex)                     {                         messagebox.show(ex.tostring());                     }                     sqlcecommand mycommand = new sqlcecommand("insert dbo.login values ('" + usernamebox.text + "','admin', '" + saltedcryps + "', '" + hashedresult + "')", myconnection);                     mycommand.executenonquery();                     messagebox.show("thanks registering!");                     this.close();                 }             }             else             {             }         else if (a == "user")         {             if (checkusernameempty() && checkifusernameexists() && checkpasswordsnotempty() && checkpasswordsmatch())             {                 {                     sqlceconnection myconnection = new sqlceconnection("data source=eventcontrol.sdf");                     try                     {                         myconnection.open();                     }                     catch (exception ex)                     {                         messagebox.show(ex.tostring());                     }                     sqlcecommand mycommand = new sqlcecommand("insert dbo.login values ('" + usernamebox.text + "','user', '" + saltedcryps + "', '" + hashedresult + "')", myconnection);                     mycommand.executenonquery();                     messagebox.show("thanks registering!");                     this.close();                 }             }             else             {             }         }      } } 

like said, gets run command part in if (a == "admin") part, stops working. when user.

info: have copied program old program, old program used sql server, 1 use sql server ce, can embed program , use on computer. not show message box, not add information database or anything, brings blank mdi screen, when supposed go login screen after adding relevant information

thanks guys