When you are done using a file, be sure to explicitly close it ASAP. This is important if the file is shared ( that is multiple users are using the same file ) - like a hit counter or something like that.
<%
Dim oFile
Set oFile = File_OpenExisting( "c:\test.log", File_OpenForReading )
If oFile Is Nothing Then
Response.Write "Not existing"
Else
Response.Write "Existing"
'Here we can start reading from it
End If
oFile.Close
'ASP Code continues...
%>