Exception: return-from-callback "scheme_stat"

While developing an application I started getting the following
exception.  What does it mean?

Error: exception
       wrong-type-argument
       (return-from-callback "scheme_stat" '<Error while displaying condition.>

For various inputs to the application, this exception might or might
not be triggered.  Once an input has been found that triggers it, it
seems to always be reproducible.  However, I can't see any pattern in
the changes to the input that would make a difference -- seemingly
equivalent inputs might or might not trigger this exception.

Using SCSH version 0.6.7 on Mac OS X 10.4.7.

p.