Removing Holes

Hello,
I am trying to remove a hole on a part, this should be done using the remove holes feature.
However, remove holes does not work for all the holes. I tried using Merge Faces, but it returns an error for unknown reason. I think it is a glitch in VC 4.2 just like Blockify or Cylindrify.
Is there a way I can remove holes or merge faces using Python?

Thanks