This is based on my experience today. Feel free to add more errors and what you did to fix them.

Error #1

DBD::mysql::st execute failed: Table './sitename_com/AnyTableName' is marked as crashed and should be repaired at /data/WebGUI/lib/WebGUI/SQL/ResultSet.pm line 135.

Solution #1

repair AnyTableName table in mysql: (referenced http://felipecruz.com/repair-mysql-database.php)

1. Login to mysql
2. > Repair table AnyTableName;

Error #2

Cannot write to '/data/wre/var/logs/webgui.log':

Solution #2

use command df to determine if you drive is full.

1. your delete log files
2. look for large files and delete as appropriate:

   find / -size +10M 2>/dev/null -exec ls -la {} \;