Unity 2d animation issue.

I am experiencing some very strange issues when I try to create a 2d animation in Unity - Firstly , when I import the animation frames (that are  numbered 001 to 095) , they import in a very strange order when the bar shown below is computing : 

You would expect Unity to import from start to finish in order , so 001,002,003,004 and so on , but it actually goes 087,034,011,002,092 ..... 

If you look at the bars above , it is importing frame 045 very early on , and then 016 much later on. 

However , once imported , all looks fine : 


The problem comes though when I try to make an animation with these frames - when I drag and drop them into the animation window, they play out of order in the same incorrect sequence that they were imported in. ALSO , some frames are skipping altogether so the animation is a complete failure. 

The animation and components are shown below : 

I have made many animations in this project and have never had this issue. I have no idea why Unity is doing this , can anybody help please?