Well, I don't see anything obvious in the test image that would cause the problem.  I agree with you on using software to increase res.  Could you post the image again, with a small X or something to indicate exactly where it gets to before it hangs?  Also if you would like, I could send you my email address and if you wanted,  you could email me the file and I could try and see if it hangs here as well.  I have a dual core Athlon64 so it would go pretty quick.