Please --

• cut your script down to the minimum (not more than a few dozen lines) that displays the problem (we usually don't need to see the un-related parts of the script that's giving you grief).
  ...and
• Clarify your problem statement

You appear to be contradicting yourself:

Although I can view the graph, and save it as png file... I cannot view it using png viewer...

Do you mean that it renders well in a browser so you can "view" it there, but not in a standalone graphics program? And how does " ...and also import it into MS word" relate? Is that meant to be part of a compound negative -- I can't view it with a png viewer and I can't insert it into M$ word?