Says wrong game version

[TwistedMaster]

I have both steam versions of FO3 GOTY and NV. Both have all DLC. Both have been run from steam once. Have TTW in a folder outside "C" drive. Both games work fine separately. Have also the 2 TTW updates in the TTW main folder. When I launch TTW installer it shows all files to install. I select the main one. A window pops up to choose locations of games. The NV path is there. So I point it to my FO3 folder. TTW in stall is showing my NV data folder. When I hit install I get a pop up saying "FO3 is wrong version" Why? It is fully updated with all DLC. And I verified the game. So what am I doing wrong? Thanks in advance for any\all help.
BTW: I don't do mod managers, never have, all the way back in both FO series and ES series. I like having greater knowledge of the workings of a game.

[pintocat]

Are you using English versions?

[TwistedMaster]

Yes

[RoyBatty]

Make sure the files aren't read only for Fallout 3. Verify your cache, if you have modified it in any way previously, it will not work.