Mee-too.
I have searched high and low for an answer to this, as so many others, but none of the tips have worked.
After hearing from several customers that they were "unable to purchase" I finally wrote "(You have to check the box to be able to buy. Bug...)" in the override for
COM_VIRTUEMART_CART_TOS_READ_AND_ACCEPTED
Not in COM_VIRTUEMART_I_AGREE_TO_TOS!