Actually, this is caused by a common "gotcha" in AA: although "pagename" is tracked with Custom/Download/Exit Links, AA doesn't actually allow Page and Custom/Download/Exit Links to be reported together!
So the solution is:
Setup an eVar to track the same value as your Page. A simple way to do this is to set the eVar to "D=pagename". AA will then copy the value from Page into your eVar when it processes the hit.
Now in your report, use that eVar instead of the Page dimension.
"The ‘Instances’ metric shows the number of times a dimension was explicitly defined in an image request. Some dimensions, such as eVars, persist dimension items past the hit they are set on. This metric is useful when you want to see the number of times a dimension item was set without the hits where that value persisted."