This error is caused when a duplicate PrintNode account exists under the same email address and will prevent you from being able to sign into PrintNode using SKULabs until you successfully authenticate with the SKULabs Print Client on your desktop.
If you came from another order fulfillment software, you may also still have their branded printer client installed which can conflict alongside the SKULabs Print & Scale client.
Uninstall any other print clients / print node installations you may have from another platform. These can not co-exist alongside one another.
Change your email on the primary (first to signup) user of your SKULabs account.
Try to log in to the print client using any user's credentials on your SKULabs account.
If you still receive authentication issues after this reach out to our team using the in-app chat to let us know.