I am using the RadSpreadsheet control

1) I use a provider to file

Dim provider As SpreadsheetDocumentProvider
provider = New SpreadsheetDocumentProvider(Server.MapPath("~/rtemp/" & l_c_fexcel.Text))
RadSpreadsheet1.Provider = provider

2) User fills info as they need
3) Click on SAVE (disk icon)
4) File saved, but is corrupted