Dear Christer,
We have tested your report at our demo site (http://oxdemo.skalfa.com/) and everything works correctly.
- We have created two roles VIP and Virtual. So, now we have three roles: Free, VIP and Virtual.
- Unchecked the 'Start mail dialog' action for all roles.
- Set -50 value for the 'Start mail dialog' action in the User Credits settings.
Gave the VIP user 100 credits and sent the message under this user account. We could send only two messages, then the system asked us to buy more credits.
This means that everything should work on your site. The only thing we can suppose is that the VIP users who have the problem, have another role that allows to send message for free assigned to their account. Please check if these users have only default and VIP roles assigned, and the 'Start mail dialog' action is disabled for both default and VIP roles.
As for the problem shown on the screenshot - this is not the User Credits plugin. This is a third-party plugin with the 'credits' prefix. Our plugin has the 'usercredits' prefix. Do you have any other plugins at your site which are connected to the credits?