how do i use iframe in 3.4.2?

I’m having trouble with iframe code in my wordpress site.

The company that developed my site were able to add youtube videos and google maps to my site without the iframe plugin. When I tried to add a google map, I get the error message:

“This content cannot be displayed in a frame
To help protect the security of information you enter into this website, the publisher of this content does not allow it to be displayed in a frame.

What you can try:
Open this content in a new window”

So I tried logging in as the admin because I thought that maybe users were not allowed to add any html. It didn’t work under admin either.

Of course, the company that developed my site is not responding to my requests for support, so I was wondering if anyone out there in WordPress world can help me out?

I’m baffled because the developer managed to add iframes without the plugin. Any suggestions?