Heyyo,
It's a known issue right now. I believe that one of the last hl1 engine updates broke the compatibility with EPB v5.3... but not fully sure since I ain't a coder.
Anywho, make sure you fully uninstall EPB v5.3 and then install EPB v5.2, otherwise you might get some leftover files from EPB v5.3 which's causing crashes for you such as the one at load.