WEBdev.webserevr blocked the excel to delete

HI

  In my ASP.net Application i did the excel Export from grid view by using EPPLUS DLL. before save that excel i want to delete the file excel if already exists in the folder.but first time the excel was Exported on the second time excel generation that excel file was not able to delete and shows the error as
"System.IO.IOException: The process cannot access the file 'F:\Test\\report.xlsx' because it is being used by another process".
and also i was not able to delete the excel as manually that time error was thrown as
"The action can't be completed because the file is open in webdev.webserver.exe".i m using vs2005 and sql 2005 with IIS 6.0

kindly do the needful to fix this error.