What version of Zen Cart?
Version V1.3.8a


When did this "start" happening?
I dont know exactly, i thought it happend because i moved the website to a new server.
But now i see it also happends on the old server.

What addons do you have installed?
admin_login_as_customer_v2-1
ask_a_question_1-8
best_sellers_page_Alpha2
better_together_2-0
categories_dressing_2-7-3
change_product_name_to_proper_case_1
cold_steel_template_v1-0
column_divider_pro_cdp_v0-4
column_layout_grid_for_product_listing_1-3-8
cross_sell__just_another_cross_sell_mod_rev186
cross_sell_advanced
css_horizontal_dynamic_menu_pauls_edition_1-1
debug_error_logging_utility_1-0
dutch_languagepack_zencart138av20081016
export_shipping_information_1-2-4
german_language_pack_20081111
google_mapinator_0-12
ideal_sitebox
image-handler_2.0-zc12
improved_attributes_controller_1-1b
improved_sitemap_display_1-0-1
jscroller_sidebox_package_v1-0-1
languagecurrency_links_in_header_1-0
Manufacturers All - 1
master_password
module_manager_rev16zip
multilanguage_ezpages_1-3-0-5v2-02
multisite_admin_tools_0.2
multisite_module_Beta0-4-1
product_filter_by_attribute_and_price_range_0-7
promo_better
recently_viewed_items_1-0
rss_feed_2-1-4
scheduled_events_1-3-8a
security_patch_v138_20090619
sitemapxml__formerly_google_sitemap_2-1-0
sitemapxml_ezpages
smart_backgrounds_2-1-1
stock_by_attributes_4-7MULTIADD
super_orders_2-0rev47
tabbed_products_pro_v1-05
utf_support_for_zencart_1-0-1
zen_lightbox_1-5
expiring sales
database cache

Website is hosted on a dedicated Server with only a few other websites.
Specs: Quadcore Intel 5310 proc, 2gb mem, sas 3gb harddrives.