If you are doing everything right, try compiling RABCDAsm from source on your computer. The only result I found of a similar problem said that that was the fix. Otherwise, make sure you are following the instructions exactly. Starting with a .swf file that isn't lzma compressed, unless you have support for that, run:
abcexport example.swf
rabcdasm example-0.abc
[make changes to the .asasm files in the example-0 folder]
rabcasm example-0/example-0.main.asasm
abcreplace example.swf 0 example-0/example-0.main.abc
It's not the end of the world if you don't get it working. JPEXS does everything RABCDAsm does, just with slightly worse workflow in my opinion. If your project is complex enough that JPEXS feels clunky, you should be editing a source anyways.