Media Encoder 12.1 not encoding

Just downloaded 12.1.  120. worked fine, but in 121 I send a timeline to Media Encoder from Premiere, and it loads in the queue. I then press start to encode the file and nothing happens. Encoder just sits and doesn't encode the file. Then I press the stop button, then I try to close AME and I have to force quit it to close the program.

I have trashed the preferences and restarted my machine multiple times, all to have the same issue.

Machine specs

MAC OS X El Capitan  10.11.6

MacPro (mid 2010)

2x2.66 GHz  6-core Intel Xeon

64 GB  1333MHz DDR3 ECC

Graphics  ATI Radeon HD 5770 1024mb

Any help would be greatly appreciated

Thanks