Are you running the script from the local client (as oppossed on remote work station?)
If the script is running on a different machine than the Excel file location then you likely need to share the remote directory which contains the Excel workbook, with either just the client machine you are working from, or for everyone.
This line:
strFileName = "C:\Automation\Sanity Testing Tracker.xls"
Would become:
strFileName = "\\RemoteComputerName\ShareDirName\...\Sanity Testing Tracker.xls"
Did you successfully create the Excel object/workbook/worksheet?