Upgrade package stuck at "Reading package lists..."

I have a single update pending for libcurl3-gnutls-7.26.0-1. When I try to install from GUI, I get the info dialog open, but stuck at the first line: "Reading package lists...". No progress from there.
Tried to kick it a few times, or reboot. No joy.

When I do "apt-get update" from CLI, it ends with the following. Not sure it's related.

Ign http://packages.omv-extras.org kralizec-vb/main Translation-en
Traceback (most recent call last):
  File "/usr/sbin/omv-mkaptidx", line 55, in <module>
    cache = apt.cache.Cache()
  File "/usr/lib/python3/dist-packages/apt/cache.py", line 102, in __init__
    self.open(progress)
  File "/usr/lib/python3/dist-packages/apt/cache.py", line 145, in open
    self._cache = apt_pkg.Cache(progress)
SystemError: E:The value 'stable' is invalid for APT::Default-Release as such a release is not available in the sources

Zitat von ryecoaaron

rm -f /etc/apt/apt.conf.d/99openmediavault-release /etc/apt/apt.conf
apt-get update

Ouch. I did see that other post, but since I saw I don't have that 99openmediavault-release file, I presumed it's not applicable to me. How wrong I was.

This worked like a charm. It's all good now. Thank you and sorry for the dup.