It looks like the skeleton definition in one of your SMD files is invalid. What happens if you compile the QC?

The fix is now available from GitHub.

The problem is that the animation defines attachments, which doesn't make any sense outside a reference mesh.

I'll make a change to ignore attachments while importing an animation.

Yes. Object animation is not supported.

Item 1 is news to me, and I will investigate.

I have previously spent a lot of time investigating item 2 but was never able to find the problem. The fact that another exporter has it working means that I should make another attempt.

You can create a new key binding which configures default values in Edit > Preferences > Keymap. Add a new binding targeting "import_scene.smd".

This seems to be a Crowbar bug: https://psteamcommunity.yuanyoumao.com/groups/BlenderSourceTools/discussions/1/2516897767695060288/

The SMD is invalid. Search through it for "-.." and replace the second dot.

I've fixed it. You can download the latest code from GitHub or wait until the next release, which I hope to make soon.

Just file a bug on the developer website, they will deal with it.