Index: wafadmin/Tools/preproc.py
===================================================================
--- wafadmin/Tools/preproc.py	(revision 1701)
+++ wafadmin/Tools/preproc.py	(working copy)
@@ -16,6 +16,7 @@
 sys.path = ['.', '..'] + sys.path
 import Params
 from Params import debug, error, warning
+import traceback
 
 class PreprocError(Exception):
 	pass
@@ -461,9 +462,11 @@
 			self.lines = lines + self.lines
 		except IOError:
 			raise PreprocError, "could not read the file"
-		except:
-			if Params.g_verbose > 0: warning("parsing %s failed" % filepath)
-			raise PreprocError, "unknown exception"
+		except Exception, ex:
+			if Params.g_verbose > 0:
+				warning("parsing %s failed" % filepath)
+				traceback.print_exc()
+			raise PreprocError, "unknown exception (%r)" % ex
 
 	def start2(self, node, env):
 		debug("scanning %s (in %s)" % (node.m_name, node.m_parent.m_name), 'preproc')