We are running a banner ad inside a Mailchimp email newsletter. The code for the ad that is being inserted into the newsletter code is takes one of the following 2 forms and neither one is working. The ad server is revive. We are using a custom modified version of revive.

Form 1: Non-escaped
<a href="https://console2.adserver.net/www/delivery/cl.php?zoneid=6&rand=*|EMAIL_UID|**|DATE:mdyu|*" target="_blank"><img alt="" border="0" src="https://console2.adserver.net/www/delivery/avw.php?zoneid=6&cb=*|EMAIL_UID|**|DATE:mdyu|*?&rand=*|EMAIL_UID|**|DATE:mdyu|*" /></a>

Form 2: Escaped
<a href="https://console2.adserver.net/www/delivery/cl.php?zoneid=6&amp;rand=*|EMAIL_UID|**|DATE:mdyu|**|CAMPAIGN_UID|*" target="_blank"><img alt="" border="0" src="https://console2.adserver.net/www/delivery/avw.php?zoneid=6&amp;cb=*|EMAIL_UID|**|DATE:mdyu|**|CAMPAIGN_UID|*?&amp;rand=*|EMAIL_UID|**|DATE:mdyu|**|CAMPAIGN_UID|*" /></a>

The ads are not displaying when the viewer opens the email in gmail. When we inspect element, we are seeing a 404 error. The image appears to be cached and when we go to the URL of the cached image we see a message that says

"That’s an error.The requested URL /proxy/DhGj_CvbjqUL6BVeEPrTHPE7MaNCnjJ... was not found on this server. That’s all we know."

When we view the email in all other non-gmail email clients, we can see the ad just fine. When we use a different ad server - which we are not able to use for business reasons - the ad renders just fine in gmail.

Any idea what might be causing this issue?