No short URL generated – API error?

I don’t think I’ve actually changed anything since my last WP post (yeah, I know, everyone says that), but today I noticed that YOURLS short URL was not generated for a new post. When I tried to generate it manually via the “Get YOURLS” button, I got the following error message:

There was an error contacting the YOURLS API. Please try again.

The API key is correct and I haven’t found any more detailed error messages in log files even with WP_DEBUG enabled. Any idea what went wrong or how to debug this?

http://ww.wp.xz.cn/extend/plugins/yourls-link-creator/