GIMP FX Foundry

When I run the sepia toning filter I recieve the following errors;
Plug-In 'Sepia Toning' left image undo in inconsistent state, closing open
undo groups.
followed by;
Error while executing script-fu-Sepia_Toning:
Error: Bad syntax of binding spec in let* : ((sepia-layer) (mask-layer)
(mask))

I'm using Gimp 2.6.1 on Ubuntu Intrepid. I also get this error with the
original script from the Gimp Plugin Registry
http://registry.gimp.org/files/sepia_toning-0.3.scm