HI, long time no see! I've unraveled the simple mystery!
Thanks for the advices.
Here's what has gotten me unable to Merge the two vertices, even if I have tried using Merge Tool or Merge Vertices. Since Im new to Maya, I've nevr found making distance above 0. that maybe a serious innocent mistake.
Thanks to PBmAN!
i FOound the answer before i Logged back in.
PBman's supposed to be a detailed advice.