Excel internal error 'Element not found

Hi 

I am working on a test case related to excel

The scenario is like that I have an excel workbook with two sheets and both are in the protected state (not password protected)

I am able to open the excel file using

excelFile = Excel.Open(CurrentFile)

but when I try to take control of a particular sheet following error is given

var excelSheet = excelFile.SheetByTitle("EQUIPMENT")

Excel internal error 'Element not found

It looks like the issue is related to sheet protection because when i repeat the same workflow after unprotecting the sheet everything works fine

The sample sheet is also attached

Below are my queries

1. How can I work on an excel sheet that is in the protected state

2. If step 1 is not possible then how can I unprotect the sheet