Tom,

We recently discovered an issue with Autodesk's RegApp Cleanup utility with the AutoCAD 2025 Update 1.1. There appears to be a dependency conflict resulting in a .NET error and the application not launching, we've notified Autodesk of the issue and they confirmed it on their end and are investigating. Until they post a solution though their RegApp tool will not work with AutoCAD 2025.1.1.

In regards to the missing DLL error when downloading the tool directly from Autodesk, in order for the tool to run you need to extract the contents of the download and place the EXE and DLL they provide in your AutoCAD installation directory and run it from there. Unless they've posted an update to the tool within the last couple days though I imagine you'll continue to run into the same issue. If you have an older version of AutoCAD installed still you can "install" the download the from Autodesk into that CAD's installation directory and it should work with that version.