[detectivemode]
From the looks of it, it is clearly a database issue.
'16777215' for key PRIMARY <--- indicates that the primary field in a certain database table has overflowed, i.e. too many entries.
Only a selection of members are having this problem, which means the database table is only used when those members logged in.
AveragePotato is not working in chat, so this could be related.
[/detectivemode]