This occurs when a PLC with a limited user policy is connected to the solution. Information on user policy restrictions on a given PLC can be found in the following table:
and search here in the Web - Multiple user policy. If "No" is specified for a given platform, then the PLC supports only one web user within the user policy.
By default, after assigning a PLC to the solution, a user policy with three users is automatically pre-prepared:
If the user is marked as Default or Admin, then it really cannot be removed and the Delete (user) option will be grayed out. In order to delete the other two users, we must select one user, which we will mark as Default and at the same time as Admin. Then the Delete option will be available for the remaining two users.
The resulting state can then look like the image below, for example. To save the changes, it is necessary to confirm by pressing the OK button in the red highlighted part under the user and then upload the solution to the PLC.