Some players have reported a launch error displaying "Invalid root in registry key". This occurs when Immersion's launcher has trouble locating your Diablo II installation folder via the Windows Registry (specifically, via the key in HKEY_LOCAL_MACHINE).
After having recently built a new PC, I found myself able to reproduce this error, and thus I created an alternate mod launcher to perhaps circumvent it for others:
This alternate launcher is backwards-compatible, and will be included with the next version of Immersion. Should the alternate launcher also fail to launch Immersion, reinstallation of D2:LoD is recommended to fix the problem.
While I'm here, I'd also like to note that while Immersion does READ your registry, it does not ever write to it or modify it. Nor should it ever do so. This keeps uninstallation of the mod simple.