Hi James,
I just started as SAP BASIS.
Hope you searched before asking ,anyways you could refer some good SCN documents related with your query and i suggest you to follow below SCN links with to resolve your issue.
1.
I didnt run SGEN, I still dont know what is SGEN.
2.
How to check those tablespaces??
How To Extend Table space on oracle
3. Run the Update stats and Analyze tables job in your DB
Hope this will help you.
Regards,