When I open muon updater, the error on the first picture appears. When clicking on "Check for Updates" the second one appears. 1. Installed new updates the day before yesterday. 2. The problem appeared after restarting. I'm not sure how to reproduce the problem, because I don't remember doing anything special before it appeared. Reproducible: Always
I'm not sure, but it seems the window appears after I install every new update. Normally, it would show "No updates available", but now it's showing this instead.
Does the internet connection work properly on your system then? Does it work with apt-get?
It seems that the bug has somehow fixed itself. At least I haven't seen it for a while. The second error is still appearing sometimes when I install updates, but trying again solves it.