Is it possible that you send us a small sample demonstrating the problem?
We are not sure what could be causing it, but it looks like you might be using AJAX for the grid operations. When an AJAX call starts, if the tooltip is located in a part of the page, which needs to be update using a partial page update, it needs to be closed, and disposed. Having an animation that slows the close functionality might have something to do with the error you got.
So far the only error that has been reported to us in this scenario is the "two components with the same ID....".
In the Prometheus Futures build released on March 25th
with a version number 2008.1.325.20
this particular problem was addressed and the tooltip works fine even when its parent element / target control are participating in AJAX update.
One thing you could try is download the just released official Q1 2008 RadControls for ASP.AJAX and see if the tooltip error goes away. In case it does not, sending us a sample that reproduces the problem will allow us to examine what is causing it and fix it ASAP.
the Telerik team