As reported here: https://forum.chitubox.com/?thread-453.htm
the Longer Orange 30 plugin does not work properly, at the end of "tmp.gf" file creation, it fails with error code -1.
I have investigated the problem under Linux and it seems that when the plugin is (about to be) launched, the "tmp.gf" file gets deleted although it was properly created before.
Here is the relevant part of the strace output:
115407 unlink("<omitted>/.config/ChiTuBox/tmp.gf") = 0
115407 lstat("<omitted>/output.lgs30", 0x7ffea1544a60) = -1 ENOENT (No such file or directory)
This is the wrong way around. The output file should be unlinked, and the input file checked for existence.
So I'd say the input and output file got swapped in the code.
I'm not sure whether this is in Chitubox itself or in the plugin, but it should be easy to fix unles already done for the next version.
If you are on Linux, the ugly but working fix for this is to halt the Chitubox process immediately after clicking "Save".
This can be done by pressing Ctrl-Z in the terminal window from which Chitubox was started. Then hardlink the ~/.config/ChiTuBox/tmp.gf.tmp file to, say, ~/.config/ChiTuBox/tmp.gf.link like this:
ln ~/.config/ChiTuBox/tmp.gf.tmp ~/.config/ChiTuBox/tmp.gf.link
After the conversion fails ~/.config/ChiTuBox/tmp.gf.tmp and ~/.config/ChiTuBox/tmp.gf will be gone, but you will be left with the ~/.config/ChiTuBox/tmp.gf.link file. You can then manually run the Longer plugin like this:
~/.config/ChiTuBox/plugin/CHITUBOX-Plugin-Longer3d-Orange30/linux_gf2lgs ~/.config/ChiTuBox/tmp.gf.link <your_output_file>.lgs30
You have to repeat this entire process for every output file you want to generate.