Dear Rajendra,
We are a group from Spain, our research is focused in creating different functional DNA nanostructures.
We have just started using computational chemistry and after doing some MD simulations I wanted to study the trajectories of a dsDNA using your tool, I think it can provide very useful information.
Unfortunately, I had issues while installing its plugin for VMD in windows 10 (x86). Even if it seems it is correctly installed: 
"package require do_x3dna
1.0"
When I execute any command "do_x3dna WHATEVER", it closes immediately. 
I have just solved the closure deleting all the "exit" words from the script but it still gives me this error:
=================== ERROR ======================
 $X3DNA environment variable is not available. 
 See below for usage.                           
================================================
I don't understand why, because I have already installed X3DNA correctly, I have used it for other analysis of a single step.
Could you help me?
Best regards,
Beñat Olave