This has to do with the way AE treats the coordinate axis of a solid layer. The face of the solid is always pointing down the Z axis, which is the blue axis in C4D. You'll need to make sure that your plane has its blue Z axis pointing in the direction you want your AE solid facing.
If the plane is still a primitive you can do this by setting its orientation to either +Z or -Z and then rotating the plane back into the correct orientation.
If it's not a primitive then you'll need to use the axis tool to rotate the Z axis into the correct orientation.