Error uploading custom Avatar

[Hektor]

When uploading a custom avatar, I get

There has been an error in the upload. Please ensure that the file has been correctly selected and that the upload has taken place successfully.

That avatar uploads and applies successfully, so I don't understand why the error. What's goin on here?

[Steve Machol]

Run the Upload Diagnostics and report back the results:

Admin CP -> Import & Maintenance -> Diagnostics -> Upload

Also, in the Admin CP, open the Server Settings and Optimization Options section and turn on the Public phpinfo() Display Enabled setting. Then provide the URL to your forums. This may help us troubleshoot this problem.