Go the Chat server configuration landing page in Designer Studio.Go to the Queues tab. Next to the queues name, there's an icon (two people next to each other) that you can click. That will show you the list of operators that are in that queue. Confirm that your operator is in that list. If the operator is there, that means that PRPC would have tried to sync those operators with the chat server. Make sure you hit Save at this point on the Chat server landing page.
Next is try to see what the Chat server thinks it has for the employees. For this, you can manually run the D_GetListOfEmployees page. Look at the employeesResponse pagelist in the response and see if the operator you are trying to login with is present in that list.
If both of those things check out, it would require further examination.