sql - Unable to connect to database C# -

i've been trying connect ms sql database through connection string in app.config, reason fails login, can't seem figure out.

this connection method:

public void con() {          string username = usernamebox.text;         string password = passwordbox.text;          bool loginfail;          sqlconnection conn = new sqlconnection(configurationmanager.connectionstrings["lagerconn"].connectionstring);          //search connstring user id= & password= , replace username , password textboxes         if (_connstring.contains("user id="))         {             _connstring = _connstring.replace("user id=;", "user id=" + username + ";");          }         if (_connstring.contains("password="))         {             _connstring = _connstring.replace("password=", "password='" + password + "'");         }          try         {             conn.open();             conn.close();             loginfail = false;         }catch         {             messagebox.show("login failed");             loginfail = true;         }         if(loginfail == false) //if login successful change next form , hide connect form         {             mainmenu secondform = new mainmenu();             secondform.show();             this.hide();          }      }` 

and here app.config

        <add name="lagerconn" connectionstring="data source=lagerserver;initial catalog=lagerdb;persist security info=true;user id=;password="         providername="system.data.sqlclient" /> </connectionstrings> 

i got exception

there's no point putting empty user id , password field in connection string @ all. leave them out altogether , rid of pointless persist security info too. use connection string builder, e.g.

sqlconnection builder = new sqlconnectionstringbuilder(configurationmanager.connectionstrings["lagerconn"].connectionstring);  builder.userid = userid; builder.password = password;  sqlconnection connection = new sqlconnection(builder.connectionstring); 

after that, don't provide generic error message , ignore information system gives you. @ exception , tell went wrong.