Printrbot machine profile error

[Joymaker]

I found an error in the default configuration for a Printrbot Simple Metal. The starting script consists of:
G28
G29
G28 results in the head going home to the back left corner, then moving diagonally to a somewhat more central location and settling there. The subsequent G29 operates in a displaced coordinate system such that the y-coordinate tries to move off the front edge of the printer and hits against the end stop.

Looking in the Repetier configuration that was provided with the printer, I find a starting script of
G28 X0 Y0
G29
When copied into the Simplify3D starting script, this works correctly.

[CompoundCarl]

You have to home the Z-axis before executing a G29. That's well documented in the printrbot firmware. In fact, if you don't, the auto-leveling can easily fail under many circumstances.

If you look through the firmware code, you will see why homing the Z-axis is required before you start the G29