Without knowing anything about your comp, your effects, render settings, version of AE, system info and other stuff we can't tell you anything. This could simply be some edge transparency issue or motionblur over a black background, but why and how is impossible to diagnose from your barely existing info.
There isn't any effect, it's only the animation.
Without looking over your shoulder the best we can do is guess.
Duplicate your layer and place it below the original and slide it to the left or right.
Create a mask on the upper layer that open a hole into the lower layer.
Position the lower copy so that vertical line is not visible through the hole cut by the mask.
Or you could apply any of several wire or rig removal filters. It would be better to find out what is causing the line and fix it in the source footage or the original project and rerender the animation.
The problem is that we only see the result in your screenshot. We don't see the timeline or the animators. We don't know where the layer starts, where it ends, how it moves. I suspect that the edge of the video has some funky pixels, which is common for video cameras. The first thing I would try is selecting the layer with the video, double click the Rectangular mask tool to add a mask to the video, press the M key twice to reveal the mask properties in the layer and then contract the mask by a couple of pixels.
Well, I got solve using geometric forms. But, thanks so much for the answer!!