Image uploader fails: "An error occurred in the upload. Please try again later."

When I try to upload certain files, the uploader appears to work but then gives the error message:

An error occurred in the upload. Please try again later.

Any file that triggers this error does not show a thumbnail in the media library and cannot be used on the site. The file I have been using for testing is 1.2 MB. I have successfully uploaded both larger and smaller images (by file size).

After googling and reading a number of threads about the problem, I have tried these solutions without success:

• Using the browser uploader instead of the WordPress uploader
• Deactivating all plugins via Admin dashboard
• Using 2015 theme
• Changing file directory permissions on wp-content/uploads and all directories below that to 744, then to 755
• Resetting my plugins manually
• Altering my Settings > Media to allow larger images (the image is 3702×2304 pixels)
• Replacing wp-admin and wp-includes with a fresh copy of each

I can successfully upload the same file if I reduce the size to 2000x1500px.

Can you help me determine what is causing this upload failure?

Thank you!