Data too long for column 'config_value' at row 1 
This means that you've either entered a welcome message that is too long (> 255 chars) or have selected a lot of forums to pull announcements/polls from. This is because I use the config table for storage. It has a 255 character limit. If you have MySQL 5.0.3 or greater, then you can increase the varchar length on the config_value field of the phpbb_config table.