In rare cases, the HSQL database which contains the tutorial data that ships with yellowfin can reach capacity; the limit is set to 2GB.
HSQL is an embedded database, and is not recommended for use with Yellowfin for anything other than demo purposes, as it has many limitations and is not sustainable in a growing environment.
You can easily export the data source details/views/dashboards/reports from this instance and import into a new installation so you won't actually lose any reporting data.
However, you can try increasing the size of the database by modifying the configdb.script (located under Yellowfindata) with a text editor such as notepad.
PLEASE MAKE A COPY OF YOUR DATA FOLDER BEFORE MAKING CHANGES
You should find a line
SET FILES SCALE
Try setting this to 8
e.g.
SET FILES SCALE 8
More information on this can be found here : http://hsqldb.org/doc/guide/management-chapt.html
Once complete, save the file and start Yellowfin.