AlumniSmita,
As I can see, you are trying to work with grid rows by using the objects you see in the Object Browser's object tree. It is not recommended to work with the rows in this way. The tree displays objects that TestComplete recognizes in the tested application. Typically, these objects correspond only to visible rows and they change if you scroll the grid contents.
I suggest that you explore your application in the Object Browser and find the test object that corresponds to your grid control. In your case, this could be WPFObject("_rootGrid"), WPFObject("_mainGrid"), WPFObject("_mainGridsChildGrid"), WPFObject("_grid") or some other object in the hierarchy. This object should have the Extended category of properties and this category should contain the wValue, wRowCount, wColumn, wColumnCount and other grid-specific properties.
Once you find the object, you can use native methods and properties to perform the actions you need, or you can try using methods and properties, which TestComplete provides for grid controls.
