[Therion] compiling error

I'm getting the same error every time I compile. it doesn't seem to effect the process as the PDF appears to be creating correctly.. Anyhow other than being annoying it means I have to switch views constantly so any thoughts? ##################### end of pdftex log file ##################### done writing xtherion file ... C:\Program Files (x86)\Therion\therion.exe: warning -- can't open xtherion file for output -- Plan.thconfig.xth compilation time: 1 sec