So, okay! I had another look at this and I'm starting to doubt that we really have a problem.
Can you go in mailchimp click on your name -> connected sites -> do you see your site there?
click on it and remove it.
Then go in the joomla backend to CMC and re-sync.
In my case the error that I was seeing was -> something with store already synced. It seems that once a store is synced - you cannot resync it.
We have a plugin for virtuemart ecom360virtuemart that syncs products, users etc when you make modifications in virtuemart. So after initial sync there is no need to try to resync the store.
I tested this and it seems to work fine. I was able to create a newsletter and to pull a product from my VM store.
Before you turn on the ecom360 plugin you would have to make a 2 line change there as well. (things have changed in the latest vm version)
go to:
plugins/system/ecom360virtuemart/ecom360virtuemart.php
and change:
require_once JPATH_ADMINISTRATOR . '/components/com_virtuemart/helpers/config.php';
require_once JPATH_ADMINISTRATOR . '/components/com_virtuemart/helpers/vmmodel.php';
to
require_once JPATH_ADMINISTRATOR . '/components/com_virtuemart/helpers/config.php';
VmConfig::loadConfig();
After that you can enable the plugin and the site should work. (if you don't do this change you'll see a white screen and your site won't work)
Regards,
Daniel