So I was setting up the managed metadata service application today and things were going fine. I created the service app, and associated the service app with my web application. However, after I added the Enterprise Keywords site column on a list to test it out, I was noticing that the keywords box was greyed out (Figured below). I couldn't specify and enterprise metadata values.
The fix is very easy. The first problem is around permissions. Even know the service app is associated with my web application, the user I'm running under didn't have access to the term store. So the first step is to grant the running user read access to the Term Store. Within Central admin, manage service applications, select the managed metadata service application and select permissions. Then grant the user (or in my case all users) read and restricted read permissions (Figure below):
You need restricted read selected to allow users to contribute terms to the Keywords term set in the System group.
The next problem is by default the managed metadata service application proxy won't be set as the default provider of terms. If this is not set you'll get an error that says "The site does not contain a default keywords termstore" (Figure below):
To set it as the default provider, select the service application proxy and then click properties. Then, check the top check box to tell it to be the default provider of terms for all associated web apps (figure below).
(you only get the red warnings if you have more than one service app set as the default)
Thereafter, you should be able to start adding keywords and managed metadata to your documents!
Phil