Just in case anyone has this problem:
There is a bug in the latest Keysight B2900 drivers. Specifically (but not necessarily limited to as I haven't been through all the code) the 'Configure Source.vi'
The ':RANG' command following after the ';AUTO:LLIM' command is out of sequence and results in an error 113 "Undefined header" being thrown due to bad syntax.
This ':RANG' command should actually follow the output level trigger command (as it was in the previous versions of the driver).