Could it be that you need to build the bootloader project first, with the same version of Creator you are using for the Bootloadable project?
hmm, good point.
But the example was packaged with
CY8CKIT-049-41xx Example Projects.zip.
Same page referenced to the actual Creator 3.020.
If bootloadable blinking LED.cyprj is loaded instead of .cywrk, .NET issues the exception instead.
After uninstalling and re-installing PSoC the example bootloader pgm loads and builts like charm.