We have just wrapped up the first release of DirectRT v2012 (v2012.4.1135). It's not posted yet on the download page but if you email service@empirisoft you can ask for a trial code to test it out--I expect it will resolve this issue.

May I also ask what version of Windows you are running DirectRT on? I ask because if you are running it on Windows XP (or earlier) then we also have another release of DirectRT v2010 that could fix this. But if it's Windows 7, then it may require v2012 for compatibility with the OS.