Hello.
I installed some programs on my newly installed Ubuntu MATE 16.04 trough Welcome/Software Boutique and although programs installed with no problems and working fine I now get this message when trying to check for updates and then using Fixes to update source list.
If I then go and disable Play on Linux and Opera ppa's I can normally check for other updates without any problems. But I would like those two programs updates when there is new version.
Hi @ele,
try this:
Thanks @wolfman, but for now everything works well so I wouldn’t change it.
Was just wondering why I got that message and then it was gone after disabling those ppa’s.
Hallo ele
I’m running UM-16.04.1
You’re not the only one. My problem was with Opera from the software boutique. I repeated the install/removal process twice to check, once using a very reputable local mirror, once using the main Canonical server.
Each time I couldn’t run a software update, either via the GUI “Software Updater” or via a terminal.
After uninstalling Opera everything was fine.
@lah7 Hallo, could you please pass this on to whoever needs to be aware of it - I’m presuming that it can’t be supposed to give these problems. Thank you. 
Sidebar::
I also tried Vivaldi from the boutique but found that it required so much CPU that Psensor displayed a temperature warning after only 90 seconds or so. I uninstalled that too.
Please do create a bug report against ubuntu-mate-welcome, that way it can be assigned a bit of urgency if this affects multiple users.
It's likely that the external repository has changed since it was added and is causing problems. If that's the case, it could be temporarily taken out of the Boutique.