Turn off "case-sensitive".

If you have MPLABX 5.35, the version of mpasmx should be 5.87... that's the last released version.
You should find it in the MPLABX install directory under the mpasmx folder, which for me is MPLABX\v5.35\mpasmx\mpasmx.exe

Run the exe, 'Browse...' to the folder of your .asm file to select the source file name, and 'Assemble'.
Works for me here.

It would probably work with just about any version of mpasmx/mpasmwin (same program) since the 18F452 is so old.