I think this may have to do with an alternative method of creating data files in DirectRT--a method which utilizes the underscore (_) as a symbol to use this method. For details, see the section on data output in the user's guide--esp. the section titled "An Alternate Method", or you can see it online here:

http://www.empirisoft.com/directrt/h...ata_output.htm

If this does not resolve the issue, please let us know.