Colin you may want to try running the WMIDiag tool and then checking the log file to see if the user's wmi files are registered. Our particular user's arent and we havent been able to easily repair them. You may or may not have a similar cause.. Its also easy to check if you are familliar with scripting..
I understand this is an old thread, but posting this here because this might help someone later.
I got same error as Anosh some time back, giving details on how it was sorted:
On QMC, the Assigned CALs tab went blank all of a sudden.
Clicking on Manage Users gave the error Anosh has mentioned
The General tab was showing all the available CALs were assigned
There were no change / restart on the server
How it was sorted:
I read in 2-3 threads that Qlikview Directory service was related to this issue.
Checked Qlikview Directory service, it showed it was up and running. However, ignored that status and I tried restarting it. At first attempt, the service did not respond, got a message the service cannot receive any control messages. After sometime, restart went through fine and the CAL listing was back.
I didn't find a mention of restarting QDS anywhere - so this is worth a try before trying the other complex options.
I just had this occur too - I'm migrating a client to new servers and had a transitional license with 5 User CALs originally, far below what their server is on. While working on other things, I got a new license with the same number of CALs they have on their existing server. However, with the other things going on, I had forgotten that I hadn't yet applied the license.
So, I added eight users to a server still licensed for 5. When the last three users disappeared (twice), I realized my error and updated the license, but most of the user functions stopped working in the QMC and I got this error.
Luckily, the solution turned out to be simple. I clicked "Clear License" on the QlikView Server license, re-applied the new license, and it started working again. I had to re-assign the CALs but that was relatively trivial.