I just tested on Arduino 1.6.5 (with El Capitan), and there doesn’t seem to be any issues compiling/uploading with that particular version, when using our integrated board manager. But there have been a few bugs resolved in Arduino 1.6.7, related to the board manager, so we recommend upgrading.
Let us know if this error was seen using something other than our integrated board manager, which Reuben posted above.
I have to admit, I didn’t do a full test of re-installing the Dash integration with 1.6.5. I simply downgraded Arduino on top of 1.6.7 and tested compiling. Perhaps it had to do with the board manager installation process.