[MarketPress eCommerce] Marketpress eway problem

I had an old version of marketpress running on vmxmagshop.com.au and I wanted to upgrade to the latest version.
I created a clone site to test - it's at vmxmagshop.com.au/test/
I was originally using paypal express and eWay shared payments
The paypal payments system works fine, but eWay shared payments sent an error message when I try to use it to check out.

The message is:
Oops! An error occurred while processing your payment.
There was a problem setting up the transaction with eWay: Invalid Credentials
I have checked with eWay and the credentials I'm using are correct, so it has to be a problem with the plugin.

So then I changed to the eway rapid plugin, got an api and password from eway, and tried that instead.
This time the credit card form came up, I could enter credit card details, but when I clicked the pay now button, I got a blank, unstyled page that just says 'username and password required'.
I've been back to eway again and they have looked at my settings and confirmed they are correct.
I've also tested the eway settings in a clean woocommerce installation, and they work.

Can you please have a look and see what is going wrong? I have even tried setting up a completely fresh WP site, with only Marketpress installed, and it still causes this error.
It HAS to be the marketpress plugin.
I've share access to vmxmagshop.com.au/test so that you can have a look.
Thank you.