Comment 27 for bug 50770

The workaround posted by GeekSmith works. However, I think this is a more elegant (and, possibly, _the_) solution:

One of the two files mentioned contains this section:
<policy group="netdev">
   <allow own="org.freedesktop.NetworkManagerInfo"/>
   <allow send_destination="org.freedesktop.NetworkManager"/>
   <allow send_interface="org.freedesktop.NetworkManager"/>
</policy>

However, the equivalent in the other file is:
<policy group="netdev">
   <allow send_destination="org.freedesktop.NetworkManager"/>
   <allow send_interface="org.freedesktop.NetworkManager"/>
</policy>

Adding the missing line to the second file, and of course adding my user name to the netdev group, solved the problem for me. Group policies are "better" than individual user policies, right?