Yo! I think I have a simple test case now:
Environment: CMUCL 19a on Linux x86, FSF Emacs 21.3, SLIME from current CVS, CLSQL 3.1.1.
Get the tarball
http://zappa.agharta.de/foo.tar.gz
and unpack it somewhere. Make sure the directory doesn't contain any FASL (*.x86f) files.
Fire up Emacs and start SLIME. Use ,cd to change into the `foo' directory. Now use ,l to load the FOO system. Open (C-x C-f) the file `foo2.lisp' and move point to the `get-projects-for-costs' line (the last one).
Now press M-. for slime-edit-definition - presto!
Hope that also happens on your machine...
Cheers, Edi.