This is a warning related to performance, not correctness. Seeing this does not indicate or explain any incorrect behavior, only the possibility of a slow query. As an aside, the vast majority of these warnings will go away in RHQ 4.8.
It might or might not be related, but I am getting a lot of these warnings when trying to open historical graphs and they do not show at all.
I might open a bug for it actually, it seems to be an issue with the new graphs.