We often hear about this message "The Tool Provider has been disabled by the System Administrator" The usual cause is that one of the 3 LTI switches is disabled. There are 3 places you need to enable LTI: (1) at the tool level, (2) at the course/organization level, and (3) at the LTI Global Properties level. Screenshots follow.
Administrator Panel -> Tools & Utilities section -> Tools
In a Course/Organization, Start at the Left Nav Menu
Administrator Panel -> Integrations section -> LTI Tool Providers -> Manage Global Properties