While accessing the Kerio Control User login, the page returns an "Incorrect username or password" error. When the Kerio Control is rebooted, the users are able to login successfully.
Error logs report the following entries:
License error: License exhausted, cannot allow another user (<username>).
License error: License exhausted, cannot allow another IPv4 address (x.x.x.x) for user (Crew VLAN).
This article provides explanations for these errors.
Kerio Control allows connecting up to five devices concurrently for each user. Before throwing such errors, Kerio Control tries to find a user in already logged-in users (Active Hosts menu), then it finds the IP address in the given user's IP addresses. If the current License usage (currently logged-in hosts) is bigger than an allowed license size, Kerio Control throws these exceptions.
As a workaround, it's possible to logout specific users or logout all users in parallel. It will free up the license size and allow the Users' login.
Note: if the second option is chosen, all users will be prompted to enter their credentials again.
If you have a huge amount of users connected concurrently, please consider purchasing the Unlimited user license. Additionally, you can configure the Guest network as the guests are excluded from the licensing count.