Sudden - Strange behavior of arcs

Hi,
I have this strange problem since today. Everything was working fine when I was last using the machine.

today I noticed that G2 and G3 for full circles gives me holes elongated in X. 
I was trying to do 25mm in diameter hole and it ended up being 25 along Y and 26 along X.

When I was using the machine before (approx 2 weeks ago) I was using the same program and result was circular. 

I was looking for some mechanical cause, like something getting loos, but found nothing.
I checked the same program on two very different feedrates 2400 and 300 to check for any inertia driven causes.
I checked backlash on X, and it came back normal, around 0,02. 

I am puzzled. 

Any suggestions?

Cris.

will provide tomorrow when I am back at the machine.