This error message has been popping up anytime we upload an image to an email (they will upload, but this error message appears).
I figured it might be an error with our code, so when I went in to validate our template, these validation warnings came up. Any idea what is going on? These templates were made by our Marketo consultant.
I'd submit a ticket to support. We get the 'bandaid' errors a bit as well, usually has to do with our VPN and it's connection to Marketo during some process; perhaps the upload process isn't playing nice with your network.
In our case, it doesn't really mean much and can basically be ignored, but since it's happening during a specific task each time, I'd submit to support to investigate.