Index: lib/redmine/codeset_util.rb
===================================================================
--- lib/redmine/codeset_util.rb	(revision 20033)
+++ lib/redmine/codeset_util.rb	(working copy)
@@ -23,9 +23,14 @@
       end
       enc = encoding.blank? ? "UTF-8" : encoding
       if enc.casecmp("UTF-8") != 0
-        str.force_encoding(enc)
-        str = str.encode("UTF-8", :invalid => :replace,
+        begin
+          str.force_encoding(enc)
+          str = str.encode("UTF-8", :invalid => :replace,
               :undef => :replace, :replace => '?')
+        rescue Encoding::ConverterNotFoundError
+          Rails.logger.warn ">>> ConverterNotFoundError (#{enc} to UTF-8)"
+          str = replace_invalid_utf8(str)
+        end
       else
         str = replace_invalid_utf8(str)
       end