That's a grid object you're clicking in, correct?
If it's a supported grid, you should be able to access and edit the data within the cell without having to click on the cell. Check the "Working With Grids" topic in the TestComplete help to see if it's one of the supported grids and see if there is something there to help you.
I have checked all those but still I couldn't edit the text box , any other solutions please .
I think you have more custom classes going on here.
This - "TLMKGridMaintenanceGridSite" - is being identified as a "window", not a "VCLObject". TestComplete doesn't know what it is, or any of the objects below it. They are all "window".
Speak to your dev team. You need to find out what the base class is. I use grids, but they are quite specific in their behaviour and there are several different types.
