@Jorma_Tuomainen Hello again.
So this is a strange one. We have seen here on the forum some datetime issues but I don’t remember seeing this exact one re broken update page.
Take a look at for example:
And ensure that python-dateutil is installed:
yum info python-dateutil
There are a few more references on the forum to datetime issues so there may be some clues via those threads (Magnifying glass in top right of header in forum).
I’ve also just answered your Rockstor 4 installer build question via support email so that’s another potential work around.
Hope that helps.