We all like OSCLASS, but most of us tend to forget the basics. So I decided to point out some tips that could help avoid many troubles.
1- Avoid using too much plugins. Use just the ones that are important for your needs.
2- Try as much as possible NOT TO MODIFY THE CORE FILES OF THE SCRIPT OR THEMES. Unless you know what u are doing and understand the risks and implications.
3- Don't do any modification in your mysql database.
4-When using plugins ask support from the developers. They are the right people to address your customisations. Sometimes you can post your query on the forum for help.
I believe there could be more to the ones pointed above, but these are basic tips that can help you avoid unecceasary headaches trust me. And remember OSCLASS is a script designed to work straight out of the box, so no need to do uneccessary tweeks that will bring troubles later on.
Gud luck.