To allow such a member to log in to Dimensions:
Choose a time when the number of active Dimensions users is as low as possible.
Login to Access Evo (Previously Access Workspace) as an Admin user.
Select Members.
Choose the member who has been set as a Dimensions User but cannot log in.
Remove their User role then click Save.
Choose the same member again.
Set them to have a User role for Dimensions.
Click Save.
Wait a while - this could be 10 minutes or possibly even overnight - then check to see if the user can log in to Dimensions.