TestComplete displays this message when you are opening a project that has Visualizer frames for test commands, and the file that stores Visualizer data is corrupted. The file can get invalid, for example, after its versions were merged by some source control.
To solve the problem, remove the corrupted Visualizer files and create the frames anew, if needed.
If you do not need Visualizer frames, you can remove the entire Visualizer folder: <Your Project Folder>\Script\Visualizer.
Alternatively, you can delete only the Visualizer file that matches the problematic keyword test or script unit. The file name is specified in the message.