Thumbnails not created: An error occurred in the upload. Please try again later.

When I upload an image when editing a post (version 3.7.1) I get the error named above after the progress bar reaches the end. The file does get uploaded, as I can see it in the media library, but no thumbnails are created. I can only see the image in the media library if I filter by “Uploaded to this post”. Here is the file URL:

http://www.ekran.org/ben/wp/wp-content/uploads/2013/10/state.delta_.png

(Note the trailing underscore)

If I insert the file in the post, this html is inserted:

<a href="http://www.ekran.org/ben/wp/wp-content/uploads/2013/10/state.delta_.png"><img class="alignnone size-thumbnail wp-image-2277" alt="state.delta" src="http://www.ekran.org/ben/wp/wp-content/uploads/2013/10/state.delta_.png" width="1" height="1" /></a>

(Note the pixel size, 1×1, prevents anything from appearing in the visual tab.)

Since the upload is working, and I can insert the file, I can only assume the code that makes thumbnails is broken. With some files I have seen the error appear once, and then a subsequent attempt worked fine. The file in the URL above seems to fail every time.

I’ve tried the following operations, none of which solve the problem:

1. Reinstall wordpress
2. Disable all plugins
3. Download wordpress and copy over all files except wp-content and wp-config.php
4. Replace wp-config with sample and changing database information

What next?