It should work with all MCUs and the STM32F373RCTx is supported...
It looks like either there was an installation problem or your custom board definition was incorrect.
- On which OS are you working?
- Where did you install System Workbench? in the standard place (C:\Ac6\SystemWorkbench) or another place?
- Could you check you can find the following file, in your installation directory:
- Could you attach (or include in a CODE block) your board definition file?