For those of you who are playing and learning about the next version of Windows Server (aka Windows Server Technical Preview) it might have come as a surprise that you suddenly started to receive below message.
The problem is that Microsoft has not yet delivered a new build and while we are eagerly waiting for that, we also need to be able to continue working in our labs. A server that is rebooting every few hours isn’t that convenient at that moment. Luckily, this weekend, Microsoft came to the rescue (or as some famous blogger said it this weekend… the cavalry is there…). During the weekend, they delivered a patch that will extend the trial period. The patch can be downloaded from here: http://www.microsoft.com/en-us/download/details.aspx?id=46447
A few notes on this patch.
First you might notice that it states you can continue using the current build until the next preview is available in May. At least that gives us more or less a data when to expect the next build.
Second, you can read in the installation instructions that you might need to use the DISM command (as seen below) in case you are using Hyper-V Server or Server Core and installed it from the ISO. This process can be seen below
Unfortunately, that didn’t do the trick. After rebooting (and rebooting, and rebooting…) I kept receiving the expiry message and when checking winver.exe I still could notice that my expiry date was 15 april 2015.
After a lot of emails exchanged on the MVP distribution lists where it was confirmed that lots of people had the same issue, although some of them had no issues at all the program managers of Microsoft confirmed the issue, and delivered us the solution.
Simply run slmgr /ato in a command prompt to fix it. This will simply reactivate your license key.
Reboot again, and your problem is solved as you can see in the next screen
One final note, depending on the installation with the ISO or VHD, you can retrieve your license key here: http://www.microsoft.com/en-us/evalcenter/evaluate-windows-server-technical-preview (The ISO doesn’t need one, the VHD does)
Happy continuation of preview testing 
Hyper-V Bear
Hyper-V Bear 