So, unlikely to be related to the Siropu add-on, then, if that isn't always a factor. But, still, whatever code you are using is falling back to a local URL or a URL that doesn't exist, for some reason, so it's likely related to Adsense. Does Adsense have any sort of fallback URL value? So a URL it can load (such as a local placeholder image) if it cannot serve an ad? If so, it might be worth checking that.Its stock adsense code - but it runs through Sirapo's ads manager. However, I have another location which is in the sidebar and doesn't run through the ad manager - and it sometimes does the same thing.