I have a 2-week-old Ultimaker2, which was printing well until it started showing some skew. Turns out that the X-shaft, which runs front-to-back along the right of the instrument was falling out of the bearing located at the front right. If I put it back in, it will eventually pop out again as the printhead moves around.
Looking at it more carefully, and after removing the motor cover, it looks like the short belt between the X-motor and this shaft are at an odd angle, with the pulleys too far forwards on the shaft. This could be pulling the shaft backwards and causing the problem. I could move the pulleys backwards and re-home the printhead, but wasn't sure if this was the correct approach.
Finally, with the machine off (and the shaft located in its bearing), I can manually move the printhead in Y fairly easily, but its much stiffer and less smooth in X.
I have some pictures, but couldn't see how to post them here.
Thanks for any help!