Repair DatabaseTiki needs a database to work correctly. If you get an error like table crashed (or similar), perhaps you need to fix this and Tiki will work as expected.
Table 'tiki_sessions' is marked as crashed and should be repaired
Please see some instructions
REPAIR TABLE `tiki_sessions`;
To avoid the trouble you can also install Tiki with (or convert later) your MySQL tables to InnoDB format (instead of default MyISAM).