Use string.ascii_letters instead of string.letters (SF bug #226706).
diff --git a/Demo/pdist/rcslib.py b/Demo/pdist/rcslib.py
index 5e79247..6d2e313 100755
--- a/Demo/pdist/rcslib.py
+++ b/Demo/pdist/rcslib.py
@@ -33,7 +33,7 @@
     """
 
     # Characters allowed in work file names
-    okchars = string.letters + string.digits + '-_=+.'
+    okchars = string.ascii_letters + string.digits + '-_=+'
 
     def __init__(self):
         """Constructor."""