I have that xpack, some files are damaged, as my 7zip says:
Textures\Bitume\Asphalte50.dds
Textures\Gravier\Gravier160.dds
Textures\Herbe\Herbe34.dds
Well, I even can't unzip anything physically...
So, maybe you had bad luck and took one of these?
By the way - using a huge xpack like this can slow down your btb's performance and also imagine if you share your project using that xpack? Maybe you can take textures you like and make your own xpack just with them?
Try to replace something using just default xpack and see how it goes.
[ed] Anyway, I think you can open the xpack in WinZip and delete these textures. But important - go to according folders in Materials folder and delete also xml files named as the textures. In other case the xpack will crash btb, I think. I did not check if the xpack works in btb, just extracted textures - WinZip allowed me to do that only when broken files were deleted from archive.