Hey Nick,
Sorry to hear that you're having issues with your SmarterTrack instance. Maybe whoever is sending you tickets switched to using an SVG for their signature image. Try going to Settings->Security->Uploads next add .svg to both lists and save.
Let me know if this helps.
Thanks,
Zach Sylvester
System/Network Administrator
SmarterTools Inc.
(877) 357-6278
www.smartertools.com