Unable to logon to Dynamics NAV

Dear All,

I use Microsoft Dynamics NAV 2016. Once in awhile my users do get the following error message when trying to login. '' You do not have access to Microsoft Dynamics NAV. Verify that you have been set up as a valid user in Microsoft Dynamics NAV.''

This happens even when the user is a valid user in the domain and Microsoft Dynamics NAV.

Does anybody have an idea of how I can get this resolved immediately.

Regards

Victor