The update notifier appeared on my system, with the information:
"An error occured [sic] verifying upgrade;
"this may be caused by held packages.
"Do NOT upgrade!
"Check synaptic or try again later."
Then there are options, the first two being:
"Open Synaptic package manager
I don't know what held packages are, or why I should care.
I opened Synaptic, but it just sat there, not informing me of anything, so I closed it again.
Change settings to what, please? And why?