I had this happen yesterday, so here is the solution in case anyone else has the same problem, and I'm not sure if it was related to the last batch of updates or not. This is the first issue I have ever had with LXLE.
I've always updated LXLE by clicking on the Updates option in the menu every few days, and installing whatever updates are there. But yesterday Update Manager refused to stay open for long enough to check if any updates are available, and closed down while it was doing so. I tried rebooting the computer but the problem remained. Trying to start Update Manager from the terminal, by typing:
revealed that it was crashing with a segmentation fault.
(update-manager:2262): Gtk-WARNING **: Theme parsing error: lightdm-gtk-greeter.css:57:23: Horizontal and vertical offsets are required Segmentation fault (core dumped)
So instead I updated the system from the terminal by running
sudo apt-get update && sudo apt-get upgrade
... and that fixed the problem with Update Manager. Now it seems to work just fine.
However updating from the terminal also revealed another issue, and although the system seemed to update ok, I noticed the following error messages while it was was updating:
Unpacking replacement libreoffice-sdbc-hsqldb ... Processing triggers for desktop-file-utils ... Processing triggers for menu ... /usr/share/menu/lxrandr: missing required tag: "section" Skipping file because of errors...
ldconfig deferred processing now taking place Processing triggers for menu ... /usr/share/menu/lxrandr: missing required tag: "section" Skipping file because of errors...
So I searched the internet and found that someone else had another issue resulting in an error pointing to the same file in LXLE. The problem seems to be a missing \ at the end of the first line of /usr/share/menu/lxrandr, and the solution is to add it so that the file looks like this:
?package(lxrandr):needs="X11"\ section="Applications/System"\ title="lxrandr" command="/usr/bin/lxrandr"
Ordinarily a backslash tells the terminal to read the next character (or space) literally, but when it's at the end of a line it tells the terminal to execute the next line as if it was part of the preceding line. So because the \ was missing, the computer looked in the first line for the "section" tag, instead of proceeding to the second line and looking for it there. This is why adding a \ to the end of the first line fixes the problem.