Device Admin: Cannot install assertion file

[aFouraker]

When trying to follow the steps to upgrade my core I received the following message:

Device Admin: Cannot install asertion file

How can I resolve this so that I can upgrade my core? 

[CodeShepherd]

Could you please tell us from which version to which you do upgrade and specify the steps you are trying to take? What do you do exactly when the error occurs?
See official instruction for updating the system app version in the release notes.

[vomtwo__]

Please check the system time. It should not deviate too much from the "real time" - some errors like the one you describe are related to this issue.

[aFouraker · Accepted solution]

This was in the process of updating a SFK4H. I didn't have good directions (which I have now). When I followed these good directions those problems seemed to go away.