System Workbench for STM32

Alec
I had programming and running working on STM32L476 for a short while tonight from System Workbench but now I've lost the ability. I can still program and run from STLInk.
The error I'm getting is:
Info : The selected transport took over low-level target control. The results might differ compared to plain JTAG/SWD
Warn : use 'STM32L476.cpu' as target identifier, not '0'
adapter_nsrst_delay: 100
srst_only separate srst_nogate srst_open_drain connect_deassert_srst
adapter speed: 1800 kHz
Info : clock speed 1800 kHz
Error: open failed
in procedure 'program'
in procedure 'init' called at file "embedded:startup.tcl", line 473
in procedure 'ocd_bouncer'

• OpenOCD init failed **

shutdown command invoked

Do you have any idea what has gone wrong?

thanks
St3v3