This is documented in the following KB article
This stopped any new users connecting the desktop.
Our licence server had 1 file installed with 7 licences are various amounts purchased through the years. Some of these were originally owned by different organisations hence the split.
We found that only 1 licence was valid for SA (subscription advantage) in the licence console. When concurrent connections for this licence were full, no more connections were allowed.
We proved that all our licences had valid SA in the MyCitrix. We tried to reallocate the licences as suggested in step 3 of the above ctx article
Verify the "SA Date" column is equal to or greater than 2010.0317.
If the SA date is prior to 2010.0317, you must allocate new Subscription Advantage Renewal licenses from MyCitrix.com and install them on your license server, or obtain a new EVAL or NFR license from Citrix.
The resolve the issue, you must first RETURN all of the licences. After they have been returned, you can allocate the licence and the SA date will now be correct.
I wish Citrix would have created some more detailed instructions for this particular step, but documentation in this area seems next to impossible.
I hope this helps
Sam Google +