"You must to select the delivery method"

I'm getting this error message now — «You must to select the delivery method» after clicking checkout. Everything had been fine, but I can't find what's changed.

My users have not been previously required to select a delivery method (I only have the default one).

Where can I find the source of this message? or is there a setting to turn it off?

Thank you

Never mind — someone had removed the default payment method (cash) from the delivery settings (http://bezumkin.ru/modx/minishop2/classes/804/)