Hi ONO.
could it be that s2member overwrites some settings of http://wordpress.org/extend/plugins/threewp-activity-monitor/? Unfortunately logins are not logged anymore. Can anyone confirm this behaviour?
I’m not familiar with that plugin, or how s2Member could be affecting it. s2Member has the Login Welcome redirection, or the OTO redirection, but the login still happens and I don’t see why it wouldn’t be logged.
[hilite path]Dashboard -› s2Member® -› General Options -› Login Welcome Page[/hilite]
[hilite path]Dashboard -› s2Member® -› General Options -› One-Time Offers (Upon Login)[/hilite]
Those redirections are like using redirect_to, which is very usual and that plugin must be able to deal with it. Video » s2Member (Login Welcome Page Conflicts?)
To verify if the conflict is with s2Member, deactivate it and try the login logging again.
If that plugin has a compatibility problem with s2Member, then you can try another login logger plugin. I’m pretty sure a user once mentioned having used one successfully.
Also, as a second point, can you recommend a tracking plugin that is known to work well with s2member?
Well, Google Analytics can be used, but I guess any tracking solution could be used. s2Member has an API to make it easier to integrate with them. Video » s2Member (API Tracking/Notifications)
I hope it helps. :)