Starson17 thanks for taking the time to test & reply. This is now the subject of a bug report
#814348. The long and short of it is that I can get it to work on both the GUI & command line on Ubuntu (Natty) - 32 bit, but it only work on the command line with 64 bit machines (two different machines). I have a few other custom recipes and builtins that run fine.
Out of interest what OS/bit combination did you test it on?