This error is displayed when you have reached the max table size for the 'events table', this table logs all Yellowfin events (e.g. login, startup etc...).
The table size limitation is only present in the evaluation/demo version.
The only resolution is to re-install Yellowfin using a full-release version.
If you are after a full version, please contact sales@yellowfin.bi and include your company information so you can be contacted by a member of our accounts team.