--- a/mercurial/localrepo.py	Thu Jun 16 01:58:00 2011 +0200
+++ b/mercurial/localrepo.py	Wed Jun 15 23:15:04 2011 +0300
@@ -272,7 +272,9 @@
 
         try:
             fp = self.wfile('.hgtags', 'rb+')
-        except IOError:
+        except IOError, e:
+            if e.errno != errno.ENOENT:
+                raise
             fp = self.wfile('.hgtags', 'ab')
         else:
             prevtags = fp.read()