I understand that this must be a MONyog question and not a SQLyog question. To I have moved to another category.
This error message is an internal MONyog message. It is MONyog that throws this – not a MYSQL server. There may be two reasons for it:
1) You have already registered as many MySQL serveri in MONyog as the license allows for
2) You are connecting to MONyog as a non-admin user and theis user does not have privilege to register servers. Note that the user referred to here is a MONyog user – not a MySQL user. Read the 'Security and authentication' paragraph of the program help for understand MONyog authhentication system.