Please check the permissions for mentioned login name in SQL server management studio make it sysadmin checkbox tick and then make Integrated Security=False
in the .config file.
Fire 2 commands on the client machine
ipconfig /flushdns
klist purge.
install kerbarose configuration manager on the client computer.
Finally, Restart client machine and main SQL server services. Run the application on the client machine. This Works 100% correctly.