Found the problem. I'll just paste in my Apple bug report. Not sure if SD can fix this or if it's being caused by some stupid bug/change in 10.12.2.
At some point, something has broken in 10.12.x. AppleScript apps saved in places such as ~/Library/Scripts/Applications/Safari/ no longer launch, but fail with cryptic error messages. If launched from Finder:
The application “___test” can’t be opened.
If launched from the OS scripts menu:
An error occurred. OSErr -10810
After a day's worth of debugging and searching for answers, I finally figured out that the problem is caused by Script Editor or Script Debugger not setting the executable bits on the actual executable (blah.app/Contents/MacOS/applet) when the script is saved in locations other than /Applications.
This was previously not the case. As it is now, the user is no longer able to run scripts saved in this manner, which severely limits productivity.
Steps to Reproduce:
1. From Script Editor or Script Debugger, make a new script.
2. The script can be anything, such as "beep".
3. Save the script as an application in a folder other than /Applications. A good place is your ~/Library/Scripts folder so you can launch it from the OS scripts menu.
4. Launch the app, either by double-clicking in Finder or choosing it from the OS scripts menu.
It should launch.
It does not launch and gives you a cryptic error that doesn't help.