IE cannot load index.php for older attachments

[rugrat]

Forum Status:
Just upgraded from 1.13 to 2 RC5

I had never before set max width or height to anything other than 0 in Administration Center » Features and Options » Layout. I'd like to do this for image popup.

Currently running Purple Love Theme http://custom.simplemachines.org/themes/index.php?lemma=2296 but the issue also happens in the core theme.

Only mod loaded is Login Verification http://custom.simplemachines.org/mods/index.php?mod=2956

Problem:
I'd like to set the width of images to be loaded within the forum to 400 (I assume that is pixels), so that larger images open in a new window instead of being chopped off and needing to scroll.
When I set the max width in Administration Center » Features and Options » Layout to 400, this appears to work on newly uploaded images. Images that were loaded within the last week and even before the upgrade popup in a new window fine. However older images will not load and the following  error message is received in IE:

"Internet Explorer cannot download index.php from mysite.com."
(of course mysite.com is replaced by my actual domain name)

If I switch the width option back to 0, the images load in the forums just fine, so I'm pretty sure the attachments are there.

Any good place to start to figure out what the issue is?

Much appreciated and if more info is needed please let me know.

Edit to add*
I get the same error message when I try to open attachments in Administration Center » Attachments and Avatars » Browse Files