Yes u have to mention "On Error Resume Next" statement in 
the beginning of the script

Generally, when QTP encounters a run time error during
running the scripts, it shows the error message in a pop up
window and the script execution will stops.

If you wish to display your own error message and you wish
to continue with the script, then we will use Err object.

We have to use "On Error Resume Next" statement before the
runtime error is returned.

The general usage of the Err object is like:

On Error Resume Next

dim fileSysObj
fileSysObj=createobject("Scripting.FileSystemObject")

fileSysObj.folderexists("c:\uday") 'assume this folder
doesnt exist
'QTP shows the error message here itself and stops
execution, if "On Error Resume Next" statement doesnt exists


If Err.Number <>0 then
 msgbox("Here it prints") 'Because of Err object we can give
our own error message
end if