Unusual IE error

I had an unusual error strt appearing whenever trying to write a new post in IE 6 or 7:

Line : 176
Char: 290
Error: Access is denied
Code : 0
and then it gives the URL of my post-new.php file.

It won’t let me type anything into the post editor, either.

I checked my permissions and they’re set the way they always have been, and I don’t get this problem in Firefox. I want to use IE, though, because Firefox gives me that ‘blank box’ glitch when I try to insert an image using the insert image button.

I deactivated all of my plugins and it didn’t make a difference. Any guidance as to haw to resolve this would be greatly appreciated.