I've moved this to BYOND Help. Here's what I suggest you try:

1) Make sure byond.exe is closed; open Task Manager and look at the Details tab, and if you see byond.exe in the list then you should kill the process.

2) Find your BYOND user data folder, which is probably My Documents\BYOND.

3) Find the cfg folder under that, and then delete localhub.db.

Okay, new first step: You need to turn file extensions back on. In Windows 10, this is what you do:

1) In the folder, go to the View menu option. This will open the accursed ribbon.

2) On the very right end of the accursed ribbon, you will see something that says Options, with a dropdown arrow. Click it, and then click "Change folder and search options".

3) In the dialog that comes up, go to the View tab. Near the bottom of the first page of options, you'll see one that says "Hide file extensions for known types". Uncheck that box and hit OK.

I maintain that whoever first decided that hiding file extensions by default was a good idea ought to be shot.

Now back to the problem at hand. Hold down Shift and right-click on one of those files. You'll see a "Copy as path" option; choose that. Now open up Notepad and paste; it should paste in the path to that file.

Does that path contain any characters beyond standard ASCII, like accented characters, Cyrillic, or something like that? If it does, we're going to have to move the BYOND data folder.

These are instructions for moving the data folder when the pager won't open at all. (If the pager does open enough that you can get to the Preferences menu, you can just do the move through Preferences | Advanced.)

0) Again make sure byond.exe is not running.

1) Choose a new place for your data to go. For instance, instead of My Documents\BYOND you might move it to something like C:\BYOND.

2) Move the folder to its new location.

3) Open the registry, by going to the Start menu and typing "regedit".

4) In the registry, go to HKEY_CURRENT_USER\Software\Dantom\BYOND. You will see a value on the right side called "userpath". Edit that, and change it to the new path for your data folder.

BYOND is not a Unicode application, and it doesn't work well with Cyrillic paths.

But if BYOND is installed correctly on your system, and I assume it is because you said you reinstalled, then you do indeed have HKEY_CURRENT_USER\Software\Dantom\BYOND in the registry. You must be looking in the wrong place.