There is a non-existent tech category in the file UpgradeParts-MSRB-ISP.cfg

advHeavyRocketry does not exist. Should be veryHeavyRocketry or perhaps experimentalRocketry?

Noted and changed to veryHeavyRocketry

At one time SSTU added a few custom nodes to the tech tree, and I think that was one of them.... (CTT may also add a similar/identical node?)