"Click here to Edit new asset category");

run this application on Windows Xp flickering is not occur while movet the mouse on edit icon. Run the same application on Windows Vista  while move the mouse on the Edit icon , tooltip is displayed with flickering. how to handle this. its very urgent for me. i want to fix my bug immediately. pls  any one can help me.

Don't change the text of the tooltip in the MouseMove event. Just set it once after the control is created, or even during the MouseEnter event.

Anyway, if you really must change do that in the MouseMove event for some reason, at least ensure that the text you are setting is different to the current one:

string text = "Click here to Edit new asset category";
if (toolTip.GetToolTip (btnAddAssetCategory) != text) {
  toolTip.SetToolTip (btnAddAssetCategory, text);
}

this should take care of the flickering.

HTH
--mc