Cannot use loginstudio

If the original 3 that come with Logon Studio work, then the problem is either with the logon you are downloading or what you are doing with it after you download it.
When you download a logon, usually it will be a .logonxp file and you just doubleclick it and it will install and show up on the list in Logon Studio.
Sometimes, the file will download as a .zip. If the person who created the logon says there is more than one logon included (such as different sizes), unzip the file and you will find the logons inside and they you can click on the .logonxp file. If it is only one logon, you need to rename the extension from .zip to .logonxp and it will work fine. A .logonxp file is nothing more than a .zip file that has been renamed.
Good luck

Actually I'm having the exact same problem as the OP.

For me, doubleclicking a .logonxp file *does* open up LogonStudio, but it doesn't add it to the list of available logons.

Loading one manually also does not add it to the list, and the Refresh List button doesn't help.

The only thing that has worked so far for me is to rename the .logonxp to a .zip, then extract the contents to a folder in the logons path directory.

So that's a workaround, but I've no idea why doubleclicking them doesn't add them to the list, considering that it does open the program.

Cheers