Image Ad Using Remote image not displaying

I had an advertiser that wanted to host their own ad copy, a 90 x 728 .gif file. I used the Ad Module's feature to for Remote image ads. The ad shows properly when editing the ad, when viewing the ad stats, and the ad stats are counting impressions; however, the ad does not display. Yes, the ad is active.

I inspected the empty locations where the ad should be appearing and the page source shows what looks to be normal code for displaying the ad, but I noticed that the height and width of the ad were set to zeros. There are several ads targeted for these blocks, a combination of other image and flash ads, and these all show properly but when this image ad with the remote image comes into play, the ad area is blank - but the ad stats are updated as if the ad were displayed.

Is there something I am missing here? I searched for this problem but could not find it any where. I tried jQuery and Javascript settings but they did not have any impact.