I've been using this Pi for a while now, and only recently this problem begins to happen:
I'm doing some programming (Geany, lxterminal, pcmanfm are running) and then suddenly the icons in lxpanel disappear and are replaced by invalid icons, and when I try to click on anything in lxpanel, I get "Invalid desktop entry file: /usr/share/raspi-ui-overrides/whatever_Program_I_Clicked.desktop"
Additionally, when I try to run a command in the open lxterminal (bash) I get "Input/output error".
System: Raspberry Pi 3b+
OS: Raspbian GNU Linux 9.9 (stretch)