The most common reason that events on a schedule would say "Call For Info" is that the Self Service Defaults state that you want to "List Only, Do Not Book" in terms of scheduled sessions. Choosing this setting allows the clients to see the events of your schedule on MemberMe, but does not allow them the ability to Self-Book. The second reason that the session would possibly say "Call For Info" is because the "Default Cutoff Times" restriction is to close to the event start time (i.e. There is a session at 1pm and the cutoff time for registration is set to 10 minutes prior to the start of the event. When trying to register at 12:55pm it says "Call For Info" because it is within that 10 minute period.)
To remedy either of these issues you will want to go into the:
Administration Tab > Self Service > Configure Default Settings.