Cart hangs when clicking on go to check out...get this error message

I get this message after clicking on "go to checkout"
2013 Lost connection to MySQL server during query
in:
[select sum(tax_rate) as tax_rate from (tax_rates tr left join zones_to_geo_zones za on (tr.tax_zone_id = za.geo_zone_id) left join geo_zones tz on (tz.geo_zone_id = tr.tax_zone_id) ) where (za.zone_country_id is null or za.zone_country_id = 0 or za.zone_country_id = '223') and (za.zone_id is null or za.zone_id = 0 or za.zone_id = '12') and tr.tax_class_id = '1' group by tr.tax_priority]
2006 MySQL server has gone away
in:
[select count(*) as total from sessions where sesskey = 'd60f1f220b761a5a176738c1a65de4b2']

Warning: Unknown(): A session is active. You cannot change the session module's ini settings at this time. in Unknown on line 0

I'm a newbie, so please be gentle.... thanks :)

What payment module are you using? The URL where this can be seen?

Payment modules currently active are credit card (default), check/money order (default) and PAYPAL IPN (which says "processing")

The URL is completeclassicpress.com/catalog.

Thanks so much!

What version of Zen Cart are you using?

using Zencart 1.3.7.

Suggest you check your template files then- they appear to be out of date.

Do you mean reinstall 1.3.7 on top of my current installation, or? Not sure what yo u mean by checking template files.

Thanks :)