Upload av fil som spökar i IE men inte Mozilla

Hello

får detta felmeddelande i IE:

The given path's format is not supported. 
Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code. 

Exception Details: System.NotSupportedException: The given path's format is not supported.

I mozilla funkar det alldeles utmärkt.

Här är lite kod för att ladda upp filen:

    Public Shared FUnction SaveDataFile(file As HttpPostedFile, filename As String) As String

        Dim saveToFolder As String = "\temp"
        Dim tmpFilename As String

        If (filename Is Nothing OR filename = String.Empty) Then
            tmpFilename = filename
        Else
            tmpFilename = file.FileName
        End If

        Try
            file.SaveAs("\temp\" & file.Filename)
            Return file.Filename
        Catch Ex As Exception
            Throw Ex
        End Try
    End Function

Formatet på text-filen är System.Text.Encoding.GetEncoding(850))
Annars kan man inte läsa svenska tecken. Text-filen kommer från en AS400-export

cya,
/PatrikB