Couple of days ago signing key expired on packages.netxms.org. I've renewed the key, but it have to be updated manually.

If keys was installed by package netxms-release (suggested way as future updates will be handled automatically):

wget https://packages.netxms.org/netxms-release-latest.deb
dpkg -i netxms-release-latest.deb

If key was installed with apt-key:

apt-key del 179C0A80CDFADDB1
wget -O - https://packages.netxms.org/netxms.gpg | apt-key add -