Some svg images having valid older thumbnails fail to have newer ones generated. For example, this one:
Error generating thumbnail
Error creating thumbnail: Invalid byte sequence in conversion input
Working, has been generated earlier.
Version: unspecified
Severity: major
URL: http://upload.wikimedia.org/wikipedia/commons/thumb/1/16/Stadtwappen_der_kreisfreien_Stadt_Münster.svg/99px-Stadtwappen_der_kreisfreien_Stadt_Münster.svg.png