If i remember right, thats the error you get if the mysql server closes the connection on you unexpectedly and then you try to use that connection to send another query. In my experience the error tends to come and go occasionally I've had to restart mysql to fix it.
http://dev.mysql.com/doc/refman/5.0/en/gone-away.html for more info.
As an off topic note, the error message always seems quite depressing to me... imagine it being said by Marvin from hitchhikers guide...