problem with change-class

[ik%nova@stc.lockheed.com (Ik Su Yoo)]

Has anyone one out there experienced problems using change-class
method?  Sometimes, I get an error saying 'NIL is an undefined
function. This happens only some of the time. I.e. evaluating the same
form (that produced the error) over again will not generate an error.
When I did a backtrace, the error was actually generated when
shared-initialize was called with nil as the argument.

Any information or patch to this problem will be greatly appreciated.
Please respond to ik@laic.lockheed.com. Thanks.

Ik