Exception from HRESULT: 0x800A03EC while using Value2.ToString

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C#

Hello All,
I came across this problem.
I am reading Text Data from Excel sheet.
I use the lines

while (((Microsoft.Office.Interop.Excel.Range)workSheet.Cells[rowIndex, colIndex1]).Value2 != null)//OK until here.:thumbsup:
{
string firstName = ((Microsoft.Office.Interop.Excel.Range)workSheet.Cells[rowIndex, colIndex1]).Value2.ToString();// exception is here.:confused:

//some more code goes here.
}

but this gives me an exception "Exception from HRESULT: 0x800A03EC".

NOTE: i am using C# and i have added micorsoft object library 11 and excel object library 11


Please help me how this problem can be solved.
I went through google where there was information about some regionaloptions but i dont think that should be a problem in my case as i am just reading text.