Ended up uninstalling Code Composer and doing a fresh install with 5.5.0.00077 - fixed the problem.
I now have C2000 Device Support version 4.1.0.6 installed. "builddefinitions2000_patch" is not installed.
I suspect that updating to Device Support 4.1.0.7 and installing "builddefinitions2000_patch" breaks Signum JTAG.