Why I am unable to move an Excel file from source folder to destination folder when running a windows service installed in IIS server?

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C#2.0

C#

ASP.NET

IIS7.5

Why I am unable to move an Excel file from source folder to d
estination folder when running a windows service installed in IIS server? Excel file data is getting inserted and also the status is changing fine but the excel file is not moving.It happens occassionally.I am getting an error message as "File is being used by another Process" I am using asp.net with c# and IIS 7.5.

code as follows:

m_ExcelClient.openConnection();

--Then fetching of data from excel and afterwards below code.

try
                   {
                       if (m_ExcelClient != null)
                       {
                           m_ExcelClient.closeConnection();
                           m_ExcelClient = null;
                       }
                       GC.Collect();
                       File.Move(FilePath, CopyDestinationPath);
                   }
                   catch (Exception ex)
                   {
                       Common.WriteTextFile(ErrorLogPath, ex.Message);


                   }