Getting problem as "Unspecified" Error and FindAllChildren taking more time

Problem 1 : Getting problem as "Unspecified" Error at while loop (at different while loop) in our script. 

Description : "refExcel" is our excel file object.
Following is an example:

var refExcel = DDT["ExcelDriver"](Sheetname);
while (!refExcel ["EOF"]())
{

}

1. Problem dosen't occure all the time and at the same while loop.
2. We are using the following code for closing the driver : 
 refExcel["Close"];
 DDT["CloseDriver"](refExcel["Name"]);


Problem 2 : FindAllChildren taking more time.

We are using FindAllChildren for fetching the child object of screen controls but it is taking more time and reducing performance. Is there any way to reduce the time for the same or any other way to find the object we want to access.

For example :

parent1. child
parent2. child

If both the child are same but the parent is different.