REQUIRE fails on Windows

In ASDF tests we try to require known modules to test the require features in ASDF. When I try to do this, I get odd errors. For example:

> (require :rt)

;;; Loading #P"C:/ECL/rt.fas"

Condition of type: SIMPLE-ERROR
LOAD: Could not load file #P"C:/ECL/rt.fas" (Error: "The operation completed successfully.
")

So here's a known module, that apparently is loaded successfully, but it's treated as an error by ECL.

ECL version 16.1.2 (git:2cb60658)

Running as ECL bytecodes. This is the version I downloaded from the web-site: I don't have the toolchain to build ECL myself on Windows.