ERROR_GEN_ZLIB_2 - Possible workaround/fix
Setting 'GrassQuality value' to 0 (zero)
<GrassQuality value="0" />
in settings.xml (Documents\Rockstar Games\GTA V\settings.xml) fixed a zlib error (ERROR_GEN_ZLIB_2) I got.
I was testing default settings.xml (I don't have grass on usually, the game worked perfectly before changing to default settings.xml so this highlighted that the error was related to some setting in the file. I tested & found that the grass setting was the culprit).
Obviously, if you like grass it's not what I would call an ideal fix but thought I would document it anyway.