I am using user manager to authenticate pptp dsl connections simply as a radius server. Can anybody confirm if I need to install license level 6 in order to support the authentications ? Or can I do it with a level 4 or 5 version ?

Please advise. Thanks.

you can do with level 4 or 5 license depending on how many simultaneous sessions that you want to have.

L4 supports 20 simultaneous sessions via user manager authentication and 200 if local database /ppp secret is used
L5 supports 50 simultaneous sessions via user manager authentication and 500 if local database /ppp secret is used


for more details see http://wiki.mikrotik.com/wiki/Manual:License