When trying to make any payment method error message

Hi,
Our store has been working great on opencart 1.5.4.1 for 3 years with no problems. Today a customer complained that he could not make a payment. No customers can make payments now!

So I tried paypal and bank transfer and when clicking continue on the payment method I just get an error message. Its seems that my customers cannot use any payment method at the moment. If anyone could advise what it could be or what to check I would be very grateful.

https://www.greenspacestore.com

The error is related with vendor commission or some vendor related module. It is not working properly. May be it is not initialized properly.
You must get that check done from your developer for this vendor module.

Thanks ever do much for the words. Can you please tell me how can I find out which module it is?

You must be knowing the vendor module installed on your store .
Assuming you are the admin.