Excel File is not opening

Dear Experts,
From yesterday onwards i'm facing a strange problem that my excel file is not opening in Internet Explorer 8. when I click on the Button it prompts  me "Open" | "Save" | "cancel" 
 
when I click on Save i get 
" Internet Explorer was not able to open this Internet site. The requested site is either unavailable or cannot be found. Please try again later. "
 
 
In Google chrome and Fire Fox it is working fine. i am using following code for opening file. These excel files are dynamically created.
 
Dim flename As String
flename = lblCompId.Text & "TestResultsCompWiseForExcel.xls"
Dim popupscript As String = "window.open('Export/'+'" & flename.ToString & "');"           
ScriptManager.RegisterClientScriptBlock(btnExport, btnExport.GetType(), "RSB", popupscript, True)
 
Please ...