One file is missing in the final distribution of Stitcher Pro and Stitcher Unlimited on Mac. This file allows Stitcher to launch external blending application (as set in the rendering dialog)
 
Please download the file here:
ftp://ftp.realviz.com/private/STU/extblend_MAC.zip
 
Unzip and copy the file into the main Stitcher directory.
- launchblend.scpt is the script which allows external links to work.
 
You need to configure the external links path. In Stitcher 5.5 (Pro & Unlimited only), click on Preferences > External links tab, then enter the path of your external blending software in the "Blending Software" field.
 
Before rendering, you must select the "External" Blending Method from the Rendering Options menu.
 
Stephane