change text of error message to be more descriptive

src/mod/endpoints/mod_sofia/sofia_reg.c

@@ -1914,7 +1914,7 @@ void sofia_reg_handle_sip_r_challenge(int status,
 	} else if (gateway) {
 		switch_snprintf(authentication, sizeof(authentication), "%s:%s:%s:%s", scheme, realm, gateway->auth_username, gateway->register_password);
 	} else {
-		switch_log_printf(SWITCH_CHANNEL_SESSION_LOG(session), SWITCH_LOG_ERROR, "No Matching gateway found\n");
+		switch_log_printf(SWITCH_CHANNEL_SESSION_LOG(session), SWITCH_LOG_ERROR, "Cannot locate any authentication credentials to complete an authentication request for realm '%s'\n", realm);
 		goto cancel;
 	}