A quick fix for image distortion (usually works)

1. Select the image itself and Break it Apart (CTRL-B)

I'm NOT saying violence is a solution to any other problem!

In most cases, this is enough. If not-

2. Make sure the image has at least half-a-pixel distance from either of the Stage's edges. (For example, if the Stage is 200x200 pixels, size the image to 199x199 and align it to the Stage centre. This leaves half-a-pixel distance at all sides.)

That's it. Hope it works for you.

This is the Macromedia page regarding the problem: http://www.macromedia.com/support/flash/ts/documents/bitmaps_shift.htm