This problem seems to occur when you have several catalogs in LR and when you restart your Windows computer you do not open the last catalog selected first.
Wolfram Orthacker
Hi Wolfram and welcome to the forum.
Do you get this issue when you’ve installed Negative Lab Pro, not installed Negative Lab Pro or in both cases?
Maybe it’s standard behaviour of Lightroom when multiple catalogs are present, depending on how you set Lightroom…
Lightroomqueen.com has a few comments on using multiple catalogs (use term to search the site) with Lightroom.
The problem always occurred when I shut down and restart the computer. The NLP plug-in then stopped working. You then have to delete the presets in Lightroom and reconnect the NLP plug-in. If I start the last Lightroom catalog first and only later the one I want, everything works normally. No problem anymore. And after ten new installations you don’t need a new serial number.
That seems to be the solution to this problem on Windows computers.