Server was unable to process request. —> Attempted to perform an unauthorized operation

need  manually set IIS authentication to use only windows integrated authentication(uncheck the anonymous authentication), and make sure you or the user account has enough rights on your search service.

queryService.Credentials = new System.Net.NetworkCredential(“username”,“password”,“domain”);

or you may want to try different passing

queryService.Credentials = System.Net.CredentialCache.DefaultNetworkCredentials;

or

NetworkCredential networkCredential = CredentialCache.DefaultCredentials.GetCredential(new Uri(queryService.Url), “NTLM”);
or

queryService.Credentials = networkCredential;

 queryService.Credentials = System.Net.CredentialCache.DefaultCredentials;
queryService.PreAuthenticate = true;