Thanks AngelinaBelle,
In fact, I've noticed that the problem is solid. ( at least for my system)
Deleted the old ones ( shoutbox)
Created fresh ones ( both shoubox and block related)
If no entry in the block, fine .. ( main pages loads properly)
As soon as I enter something ( Like "test", no special character) in the shoutbox, and try to load the main page, facing the same failure. mysql has gone away ...
Seems some settings for shoutbox in the DB somehow corrupted.
I hope it's clear..
DB entries attached