Windows 10 preview started to nag me because it wasn’t activated. Trying to activate it only resulted in an error. When clicking error details it showed error code 0x8007007b.
The way to solve this was to click change product key and enter this key:
I had to enter it twice before the change worked. After this the activation worked. Almost, I didn’t get an success from the activation, I only got a white blank window. But after reopening the windows the activation was ok.
I was running preview build 9926.
And it looks like it is the same problem, and the same solution, in build 10041.