I had this problem same earlier today and deleted the Updates.db file as advised. Logos started fine.
Then I went on to try to deal with my bigger problem of my system crashes (Logos tech thought it is a OS problem, not caused by Logos)
I ran disk utility first aid, which found several disk permission problems and repaired them.
Now Logos will not open again.
I tried removing the Updates.db file, but that did not help. I reinstalled the Logos5 engine, Logos still will not open. The "signing in" notification appears for a few seconds, then startup fails.
3683.LogosLogs.20130419-204751.zip