First, make sure that you have no other files open besides DirectRT itself before trying to run anything in DirectRT.
If the problem still persists, make sure that all of the files you want to run in DirectRT are located somewhere on the same hard drive on which DirectRT itself is installed.
Please feel free to send me a copy of all the files that you are attempting to run in DirectRT. You can either upload them here or send them directly to support@empirisoft.com. You may need to use a file sharing service like Dropbox or Google Drive if the total size of the files is large enough. Please reference case 25536 if you use email.
Please also tell me the full version number (i.e., 20xx.x.xxx) of your copy of DirectRT. You can find it by opening DirectRT and selecting Help>About DirectRT from the main menu bar.
Jason Reed
Empirisoft Software Support Specialist