Steel Bank Common Lisp

Greetings,

Suppose I make a directory (e.g., mydir) on a Linux machine 
(e.g., lmachine) available to an MS Windows machine via Samba.  
On the MS Windows machine, I can type "cd //lmachine/mydir" in 
a cygwin or msys shell window to access that directory.  But
(probe-file "//lmachine/mydir") returns nil in SBCL win32.
Does anybody know how to access files on a network drive with
SBCL win32?

Best,

-cph