Ensure that SWD interface is enabled in the project as Debug Select to SWD in the .cydwr window.
Reduce the path size, preferrably unzipping the workspace archive in Desktop.
If it does not help, please share the project and PSoC Creator version to recreate the issue at our end.
Yes, Debug Select is set to SWD.
The project is in c:\projects, so the path can't get much shorter.
I am using the latest version of PSoC Creator (18.104.22.1681) on Windows 7.
How can I share my project privately with Cypress Support?
Thanks to FAE Kevin Reed for solving this.
Performing "Clean and Build All Projects" solved the problem.
The issue was caused by the .hex file for the Bootloader project not getting updated. Although I had done a "Clean and Build [MyMainProject]", and "Build All Projects", the Bootloader project had previously been compiled with Code Protection enabled and the .hex output still contained this setting, which prevented the main project from being debuggable (hence, did not show in list of targets).