AGB problem with MySql

I use AGB 2.3.1 for a while now, but suddenly few days ago no more GB! Instead I have the following msg:
MySQL Error : Query Error
Error Number: 1104 The SELECT would examine too many records and probably take a very long time. Check your WHERE and use SET OPTION SQL_BIG_SELECTS=1 if the SELECT is ok
what's strange is that the admin panel works fine, I can see all the messages; I still can post msg in the book??? As I didn't find the SQL_BIG_SELECTS thing in the php/mysql manual, I am calling for your help.... I only have 277 msg in the data table!?
Please help!!

I have the same problem. One year the guest book worked normally and now instead of the main page I see it:

MySQL Error : Query Error
Error Number: 1104 The SELECT would examine more rows than MAX_JOIN_SIZE. Check your WHERE and use SET SQL_BIG_SELECTS=1 or SET SQL_MAX_JOIN_SIZE=# if the SELECT is ok
Date : Wed, February 18, 2004 22:30:18
IP : 62.117.108.65
Browser : Mozilla/4.0 (compatible; MSIE 5.5; Windows 98 )
etc.

Who be faced such problem?
Help, please.