To add to DJed's post:
In the particular example posted, you don't need the Merge Errors.vi at all because there's no reason to merge a guaranteed "no error" with the other error stream.
Or, to phrase it another way: BOTH "ERROR OUT" TERMINALS RETURN THE SAME VALUE. So you never have to merge these two error streams. Automatic error handling is satisfied if you wire either one of these two error terminals.