The installation of SQL server agent is disabled on full edition of sql server 2008R2

Practically overnight, the SQL Server agent that had been working for over a year failed on a server running SQL Server 2008 R2. When attempting to restart it, it fails immediately with the message

"This installation of SQL Server Agent is disabled. The edition of SQL Server that installed this service does not support SQL Server Agent."

But it is a full edition, and as I've said, its been working fine for over a year. Perhaps on a related note, the same day the Agent first failed, we also started seeing:

"License Activation (slui.exe) failed with the following error code: hr=0x80072EE7"

I know slui is a windows activation related service, could it be related to SQL server suddenly thinking it's an express edition?

The first place I would start is the SQL Server Error Log. What does it say?

Your @@Version stated it was Express. I doubt that is incorrect. By default, database mail, SQL Server Agent, and many other features aren't able to be installed or enabled easier in SQL Server Express Editions. This is why it's Free.

Some people have shown how to get around some of these limitations, especially database mail. Perhaps someone did something similar for SQL Agent, and now Microsoft has figured it out. Or, someone downgraded your server.

You can check the installation date by running the following snippet provided by Pinal

SELECT create_date
FROM sys.server_principals
WHERE sid = 0x010100000000000512000000

Note, there is no Full edition. There are:

• Datacenter
• Enterprise
• Standard
• Web
• Workgroup
• Express