Starting with Pro Tools 2021.10, Pro Tools uses a newer version of PACE iLok for launching PACE wrapped plugins. However, it does not work with plugins that were PACE protected with PACE’s tools from a few years ago. SoundCode LtRt Tools 2.1.1 and earlier is one of those plugins.
We have released a new build of SoundCode LtRt Tools, 2.1.2 that solves this problem. You can download it by following this link.