This happened after I got this advice from Adobe:
Launch ADE • Help -> Erase authorization.
• ADE will be de-authorized.
• Now again click on Help -> authorize computer.
• Authorize ADE,
Please test the issue and if it is still not resolved, please try the following steps
• Choose Start > Run.
• In the Open text box, type REGEDIT and then press Enter. The Registry Editor opens.
• In the left pane of the Registry Editor, locate the following registry key:
• Right-click the Adept key and choose Delete.
• In the Confirm Key Delete dialog, click OK.
I was not able to do the first (that option did not appear under 'help') so I followed option 2 and edited my registry, deleting the Adept key. I get the error message above even after a reinstall of AED v3.0.
Check the time, date and timezone. On of this are cause the error.
The problem seems to have resolved itself. No idea what caused it or what fixed it.
The important thing is that yes, it is now.