I'm adding this section after visiting my website analytics database and seeing how some people find my site on the web. Sure, I might get more hits to my site by adding info, but I don't care so much about that. The last person to find my site used the search words "create dds realflight".
Anyone with a newer NVIDIA graphics card or up-to-date drivers on a slightly older NVIDIA graphics card may experience an error within Realflight G5/G5.5 while generating the .dds file, if the .tga (texture file) is larger than 2048x2048 resolution. The problem is more prevailant once Realflight has already been running for a little while, having different airports and aircraft loaded and if the aircraft you imported has more than one .tga (up to two additional for specular and normal mapping.)
This issue appears to be a problem unique with G5/G5.5 as I, along wtih others, do not experience this problem with G4.5.
So, what do you do? Several things can be done. First, to import your aircraft, do so just after loading Realflight. After importing an EA with a .tga size known to be 4096x2096, restart Realflight before selecting the aircraft in the selector. This is when it makes the .dds files. Also, you can turn off normal maps, which helps a lot.