SW3STM32 Fw_F4_V1.9 CDC-Standalone success but CDT issues
Many thanks for the quick response - you're right, it cleared itself up after I left it running for some period - I went away and came back 4hours later.
BTW followed the instructions for ST-LINK to SWD to pyboard.org STM32F405 and worked nicely. Will do a post on it tomorrow.