I had the same problem. Using 3.5.1.
I deactivated, reactivated wassup, then went into options and reset all back to default.
It works now and shows visitors in “latest hits”.
Hope it helps, cheers.
For future reference,
I solved the issue (now scoring around 1000 Queries/Sec) by tuning mySQL setting to recommended values for wordpress.
Search the web for “wordpress recommended mySQL settings”
Hope this helps.
