Something similar happened to me this was suggested by Vit3D and it worked:
I think there is some problem with file type association in your computer.
.rdl file should associate with RLCntDownloader.exe, which located in SYS:\Program Files (x86)\Common Files\Reallusion\Downloader\
Try to use "Open with.." from context menu. Hope this will help.
If you wanted to review the info it is at:
http://https://forum.reallusion.com/Topic97756-231-3.aspx#bm107415
It worked for me - I hope it works or you.