409 error (Conflict) when trying to insert an image into a post

I’ve uploaded a WordPress site to the live server and I get this error whenever I try to insert an image into a post:

Conflict
The server encountered an internal error or misconfiguration and was unable to complete your request.
Please contact the server administrator, root@localhost and inform them of the time the error occurred, and anything you might have done that may have caused the error.
More information about this error may be available in the server error log.
Apache/2.2.0 (Fedora) Server at www.sitename.com Port 80

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Just to be clear – the error appears only when i try to insert the image into the page. I can upload it to Media just fine. Also, it happens with external images as well as local ones. It seems enough to have an IMG tag with something in the SRC attribute for this to happen.

It’s very weird, I’ve installed WordPress on many servers and never had this happen before.