my guess would be that for some reason (i will check if i can reproduce this somehow)
your localization strings in wppizza->localization got overwritten with the settings from the preorder plugin)
so if you go to
[www.yoursite.com] /wp-admin/edit.php?post_type=wppizza&page=localization
and scroll down to “Shoppingcart” you will find this there , instead of the defaults
so if it says <span class="wppizza_cart_preorder">currently closed – pre-orders only</span> somewhere in one of those text boxes, simply overwrite this with “currently closed” (or whatever you want to say )
let me know if my assumption/guess is correct please