Unable to toggle Time Machine on Have been backing up an iMac to Time Machine on an USB drive for some time.

I now find that in the System Preference for Time Machine the toggle for OFF/ON is grayed out and cannot be shifted to the ON position.

Selecting "back up now" from the menu still works fine.

The user is an admin, running 10.9.2.  The user login is managed by Active Directory (I know very little about this, but my Windows admin assures me that they have no policies in place that should stop Time Machine from working).

I have two machines that are exhibiting this behavior, one has had it for many weeks the other just surfaced.

Problem persists across restart, and permission repair.

Update to add:

I've tried the following at the command line:

sudo tmutil enable

And have also downloaded, installed and configured Time Machine Scheduler

Neither was a path to joy for this issue.
Turns out that Time Machine was being blocked by Active Directory policy configuration after all.