Attempt to readd the images to the ereceipts. If the error persists and you're hosted by Blackbaud, Click Chat with Support and reference this article. Please be prepared to share the following information with Support:
  • URL of the donation form in question
  • Username/Password of the NetCommunity site
In the interim, you may consider uploading the images to an external source, like Google Drive or Imgur, and then drag/drop the image into NetCommunity. This external image will allow the image to successfully display in the Ereceipt. 

An issue can also occur if the Load user profile on the app pool as been set to false.  This has been been seen on some clients in the Vancouver datacenter.  Submit a subcase and request the load user profile on the app pool be set to "true".  No SSL errors will be seen on the error logs for these cases.