Google finally admitted to a Google Maps bug that disabled the capability of zooming in or out of the map. A Google Maps Help thread explains that the issue happens when you try to embed a map using the iframe feature and that the street views man overlays on top of the zoom buttons, making the zoom buttons inactive.
Here is a picture from someone in the forums:
As you can see, the street views peg man lays almost on top of the zoom buttons. That is the issue.
Google, after about a week of complaints, finally chimed in saying:
Apologies for not hopping in here earlier in the week. I escalated this issue and it has since been resolved, as some of you have noticed. Thank you all for your persistent reports, and sorry for any convenience this temporary problem may have caused!
I personally tried to replicate this and when I did, I noticed the street views man was gone from the embed feature - so maybe this is a temporary solution?
Forum discussion at Google Maps Help.