This occurs when the link added to an image contains the session id. To resolve this, relink the image without the session id.

For example in a donation form: https://www.kintera.org/AutoGen/Simple/Donor.asp?ievent=111111&en=6fKBJLMnH5KKIVOqG4LGLXPHIiKHJWNBKbJGKXMIJtG would become
https://www.kintera.org/AutoGen/Simple/Donor.asp?ievent=111111