System Workbench for STM32

Hi,

I had the same error. I tried nearly everything. In the end it turned out the easy solution is to press the reset button on the evaluation board at the moment you start debugging!
At least if you made sure before, that the connection with you cable works (for example updating drivers with the software from this site: http://www.st.com/web/en/catalog/tools/PF260217# )

I hope this is the solution for you as well!