Previously activated users now getting "Product not activated"

Question

We have Office 2010, and use MAK keys for activation. Today we've had 4 users who were previously activated (for a couple of years) say that they're suddenly getting the "Product not activated" message. A look at MS EOpen license page shows that
we're not out of licenses. We can get it working using the elevated command prompt "cscript ospp.vbs /act" but I'd like to know what's going on. It would be great if I could fix them all and prevent future recurrences.
All of the machines are Dell laptops with Windows 7.

Answer 1

Don and Greta, thanks for your prompt responses. I spoke with MS Activation Support, and it appears our KMS key was blocked. This is likely because of our "divorce" from our parent organization; I expect they used their KMS key (legally, we owned
our own licenses but I believe the umbrella org can use the same key for all children).
Rather than figuring out how to set up a KMS server for some, but not all, of our machines, I figured I'd convert them to the MAK in my organization's name. I made the following script (and another for 64-bit machines):
cd C:\Program Files\Microsoft Office\Office14
cscript ospp.vbs /inpkey:XXXXX-XXXXX-XXXXX-XXXXX-ZZZZZ
cscript ospp.vbs /act
When I run this from the cmd prompt (as administrator) it runs fine; at the end it says "product activation successful" with ZZZZZ as the last characters. However, when I run any audit program (Kaseya or Belarc Advisor) it shows that the old KMS
key is still there. This has been the case on at least 8 machines.
When I look at MS Volume Licensing page, I now see 8 new activations on the key that ends in ZZZZZ. Is there any way to make the machine reflect that it is using a fully licensed MAK? I did try restarting, and I ran the batch file while all instances of
Office were closed.
Thanks.