if using DBC or DBPro,
the issues are the same:
1 - DB assumes ninja.x is animated (perhaps the idle animation?)
2 - before appending animation, use the command
Get Total Object Frames() or something like that ...
Lets call this number Idle_End
use this number (or -1 from it) in the append object command
also, did you make the .dat file from the save animation command?
Which animations are included in the .dat file ?
3 - Then call Get Object Frames() again for the walk animation
and call this Walk_End
4 - Loop the animations ....
to loop the Idle Animation ...... loop object ninja,1,Idle_End
to loop the walk ......
Loop Object ninja,Idle_End+1,Walk_End
Watch out for the "gotcha" problems:
If the model (.X) have different limbs or bones or names or sometimes source textures, there will be errors in the animations.