Light creates a line when merge.

Hi, this is the first time I post something here, sorry if is not the correct place to do it.

I have a light render that I make from maya, I did it using the RGB channels. Next I split the channel with a bmp node, next I pass it for a control matte, to try the adjust the alpha.

The problem that the image generate a line when i do the merge. How can I fix this? is there a better way to do it?

If maybe I'm not been clear, please ask me.

Thank you in advanced.