having a frame rate problem

What does the distortion look like? If the camera or the subject was moving, you might be looking at rolling shutter distortion. Any camera that does not have a global shutter will experience rolling shutter problems to one degree or another. The link in the first sentence is just one of the articles found on a quick search on rolling shutter problems.

Post a frame, and we will be able to see if the distortion you are experiencing is a rolling shutter problem or a frame blending issue. Frame blending problems are almost indetectable if you only slow down the footage by 50%. If you change footage interpretation from 50 fps to 25 fps, you will see every frame in a 25 fps comp, but one second of real-time will be two seconds of screen time. You end up with a slow-motion shot.

If you drop 50 fps footage in a 25 fps comp and leave frame blending off, you will see every other frame, there will be no distortion, and one second of real-time will be one second of screen time. Any available frame blending modes will create almost no discernable distortion or blurring on the shot.

Change the footage interpretation from 50 fps to 12.5 fps and drop the footage in a 25 fps comp or use time remapping, or fiddle with speed changes, and the frames will be blended in some way to fill up the holes in the timeline. Only every fourth frame will be an original frame. The other three must be blended in some way. One second of real-time will be four seconds of screen time.

After Effects (or any NLE, blends the frames by averaging the luminosity and color between the frames, which is called frame blending, or the movement of image details will be predicted, and a vector path of those pixels from the original first frame to the original second frame will be calculated. After Effects does a good job at speed reductions up to about a five or six-time slowdown, or by fixing low frame rate footage in a higher frame rate comp, 3rd party effects like Twixtor Pro can achieve amazing results when slowing down footage 10 or 20 times. The human eye has a very hard time perceiving the difference in footage running between about 18 or 20 frames per second and 60 or more because your eyes also have motion blur. The effective shutter speed for normal human eyes is a little less than 1/50th of a second. If the human eye's effective shutter speed and frame rate were higher than a 50th of a second, we would have a terrible time watching movies or television. Neon and Floursncent lights would flicker, and cheap LED lights would drive us crazy. 

I hope this explanation helps. I would be very surprised if you are seeing rolling shutter problems.