Thread:Project:Support desk/MW 1.19 - LocalS3Repo - Thumbnails issue/reply

Perhaps extension:LocalS3Repo hasn't been updated to deal with recent changes to how MediaWiki deals with filerepos that was introduced in MediaWiki 1.19.

The error message seems to indicate that image magick is having trouble finding the file in question.

You could try asking at extension talk:LocalS3Repo (although that doesn't seem to be monitored), or tracking down the author of said extension.