Thanks for the report, Karine.
Seems the error was triggered by some missing space between --counter=2 and the test input test2240686269.c, so the behavior was expected.
I got the following crash while reducing a program (I attached the relevant files + my script):
/usr/lib/x86_64-linux-gnu/clang_delta --transformation=reduce-pointer-level --counter=2test2240686269.c
Error: Unsupported file type!