RPC Endpoint 6001, and why I couldn't ping it

Look, I love Exchange 2010. As a matter of fact I'm pretty sure Bono is busy installing it somewhere in a attempt to cure World Hunger. It's like caviar, dipped in celery salt and served from Uma Thurman's belly button...but geez Louise, it can be a frustrating beast at time as well, sometimes through no fault of it's own, as we'll see below.

There my Exchange 2010 was, humming along nicely, I already moved the mailboxes across, configured Autodiscover, Outlook Anywhere, ActiveSync, all those highly visible, nice to haves. I created a test account, tested all the remote services, and it worked beeeautifully! So with a flourish I sent a mail to the client, giving him the go-ahead to roll out the remote / mobile services to his users. Only to hear back from them 10 minutes later that bugger-all remote services works. Godammit. No OA, no AS, no OWA, nada, zip. After wiping the egg from my face, I started troubleshooting. First instinct was that I somehow fudged my ISA Publishing rules, but no, it was all good. I then headed off to the bestest Exchange Connectivity Troubleshooter in the history of the world. I ran a test or two and it told me in no uncertain terms that:
Attempting to ping RPC Endpoint 6001 (Exchange Information Store) on server exc.clientabc.local
Failed to ping Endpoint
Tell me more about this issue and how to resolve it
Additional Details
RPC_E_ACCESS_DENIED error (0x5) was thrown by the RPC Runtime

Now the interesting thing here was the fact that it was only doing this for existing users, newly created ones worked without a hitch. I had a antacid (for some reason troubleshooting permission issues on IIS gets to me) and got to work. Suffice to say that I compared IIS permissions, folder NTFS permissions, even user properties in ADSI Edit. I ensured the new users had exactly the same group membership as the existing ones, everything. Then my eye caught something in the security log, All existing users, when logging on via any remote services, threw a EventID 534 in the Security Log; The user has not been granted the requested logon type on this computer.

I was making progress! a Quick review of the existing users account properties revealed that users were only allowed to log onto their workstations. The new test accounts that I created had no such restriction of course. Once I removed these restrictions from the user accounts everything worked flawlessly!

P.S. I tried granulizing (is that even a word?) the logon restrictions by allowing the users to logon to the Exchange 2010 Server. This fixed the OWA, but OA and AS was still not working. The only way I could get OA / AS to work was to remove all logon restrictions.