Update Error - release is not valid yet

[Şerban S.]

Looks like there is a problem at the repository end.
It should get sorted out so try again in 24 hours.
If it is still a problem after that, please post back.

Yes, there is.
The problem is that many repositories, mostly the PPAs, have a long cycle of shifting from the security level RSA1024 to RSA4096.
This triggers a warning related to the encryption security level, which in turn breaks the graphic update script.
The same happens when you trigger a Synaptic Package Manager installation, at the sources update step.
However, I used the CLI to update and it works fine, both in LL 6.6 and in LL 7.0.
The warning is still issued, but the update goes on without breaking.

Obviously, some of the PPAs might still break the update, if the appropriate version for the current OS release is missing.
In this case, the only way to update will be to disable the PPA that lacks the appropriate version.
In time, if the required version is released, the PPA can be re-enabled.

Best regards, Șerban.