can't import midi

I have two identical midi projects (same content, same vsts, etc). I can import (and drag) midi clips into one of them but not the other. In the problem project, when I go to import from the file menu, I choose the file and the dialogue vanishes, just as it normally would, except the clip doesn't show up in the track. If I try dragging the clip into the project, I get the cursor with the plus sign as usual, but, again, the clip doesn't show up. Won't work for any track in the project. Works just fine in the other project. Is there some setting I don't about that's preventing this?