Quoting Sean Champ (gimmal@gmail.com):
I was trying to build CXML, when I encountered an error from ASDF -- something to the effect of "NIL is not of type REAL" -- that indicating a problem in regards to a component's pathname, within a system definition.
This known ASDF bug existed in either SBCL or cclan CVS for a short period of time, but should be fixed for months now.
d.