Hi,
I couldn't find any plugin with that name "PS bPopup Messagebox" when searching on internet.
One thing I can say tho is that there is no setting to not display error messages. The point of these messages is to be displayed so that you understand what's going on.
Regarding your screenshot, it looks like your thank you page of HikaShop has been customized to display inside a popup.
That's not something done by HikaShop by default. If that's what you're talking about, I'm afraid we won't be able to help as we don't know how that modification has been done.