I am afraid that your explanations are not enough to fully understand what is actually going on. What I can suggets is to try replacing the RadToolTip with a simple DIV or panel element and to see whether the content will be dispayed there. If the problem still exist, it is not directly related to RadToolTip but to your custom logic and once you make the scenario work with a RadToolTip, you can simply put back the tooltip.
If the scenario works OK without the tooltip but the problem occurs only when you use teh tooltip, please prepare a sample, stripped down, fully runnable reproduction demo and upload it somewhere in the net and also provide a url for download. Please, note that you shouls either put a Trial version of RadControls or do not put a dll at all, just tell us which is your version. Once we are able to run a reproduction demo on our side, we will examine your particular setup locally and we will do our best to help.
the Telerik team