Page Redirect Problem

Hi,
One of my users just notified me of an issue which does not show up with admin login, but is a disaster for my site.
When a user logs-in, they are getting redirected to https://www.psocdeveloper.com/wp-admin/admin.php?page=premiumpress and it displays the error message: You do not have sufficient permissions to access this page.
When I type in my website address again, it shows that the loging was actually successful. But this is turning down users and causing almost everyone to try and reset their passwords, etc…disaster to be in with too many users.
I am not sure where this page came from. When i log in as an admin, i get redirected to the “My Account” page which is where it used to be for all users.
Can you please help?

The website is http://www.psocdeveloper.com

Thanks,
H-