AlumniHi Lane,
What grid control are you using? If it is supported by TestComplete, you can try simulating clicks with the ClickCell and ClickCellR methods provided by the test engine for supported grid controls. Parameters of these methods let you specify the row and column for the click/right-click. This approach seems more reliable than using coordinates.
Also, you wrote that you could select a row in the grid using the grid's internal methods and properties. I was wondering if there are methods or properties that let you obtain coordinates of this row. If the grid offers such methods (properties), you can use them to simulate mouse clicks.
You can find more information on working with grid controls in TestComplete help:
http://smartbear.com/support/viewarticle/13207/
Also, you can search for code samples in the How To section of our web site:
http://smartbear.com/support/howto/
