I had a look at your files beowulf, and, they are sized wrong.
The pictures should be sized in powers of 2.
For instance:
512 X 256
512 X 512
64 X 128.
etc etc
For your front and side views I suggest resizing to 256 X 512.
For the top view try 512 X 512, also your top view is angled, this might cause problems, I'm not sure if oxygen can rotate texture or not, or indeed if it will work.
Try orienting it in a North-South or South-North direction.
I'm not sure, but maybe the others have the same sizing problems.
There are many threads on this forum that have answered these problems for the greater part.
Try searching the forums next time.
Planck