i keep getting this message about twice a day

2006 MySQL server has gone away
in:
[SELECT * from zen_paypal WHERE order_id = 601 AND parent_txn_id = '' AND order_id > 0 ORDER BY paypal_ipn_id DESC LIMIT 1]
If you were entering information, press the BACK button in your browser and re-check the information you had entered to be sure you left no blank fields.
2006 MySQL server has gone away
in:
[select count(*) as total from zen_sessions where sesskey = '0sqoi43v8ksqa57qh0jj9i8bp1']
If you were entering information, press the BACK button in your browser and re-check the information you had entered to be sure you left no blank fields.

i some times get this message too
10408 Express Checkout token is missing. - Express Checkout token is
missing.

i am getting a confirmation email from paypal but i am not getting no customer order or notification from zencart, i have optimised my database ,any ideas please


steve