oh I think he is trying to paste the imgur (embed) link directly into the editor (which often doesn't work).

You need the link address for the image, not any of those special forum embed links, etc

Then when you are in the post editor, click the little picture icon above (5th from right) "Insert Image".

Once you click it, make sure you are the "By URL" option (second icon that looks like a chain).

Oh, by the way, make sure your flashing text cursor is already in the place where you want the image to appear.

For example before or after certain text.

After you add the image, you'll also get the option to insert just a thumbnail, or the full size image.

[ATTACH=full]143762[/ATTACH]

As far as imgur goes, imgur image links are notoriously unreliable. Just my opinion.