I've been having the exact same problem with the "information" message. The entire message reads as follows:
"Oops! An error occurred during the last update. Now finishing the update. This process make take 10 minutes to complete, depending on the internet. Please wait..."
I've had the Piper sit quietly for the last hour and the CPU usage monitor setting remains mostly at 0% and spikes to 2%.
Following the above instructions in the terminal, neither "apt-get" nor "pcmanfm" appeared at all.
Is there a way to download and perform the update without loading Piper from the Raspberry PI GUI?