Intermittent 404's in IE when clicking entry detail, Firefox ok.

I have the weirdest thing happening. I thought I had seen it all and that I’ve done this for a while, but obviously not long enough.

I have a directory with entries that when clicked on bring up a lightbox window with details for that directory entry on the front end.

This works flawlessly when clicking on all my entry detail links in my directory in Firefox, but occasional (yes, it’s intermittent) entries in IE 9 (with or without compatibility mode) give me a 404 error window inside the lightbox. If I close out the 404 error lightbox and keep trying to click on the same entry, it eventually comes through and the entry details show up, usually after 4 or 5 tries.

When debugging I see the following:

404: http://www.website.com/wp-content/plugins/gravity-forms-addons/entry-details.php?leadid=249&form=1&post=761&KeepThis=true&

Any ideas at all what is going on here or has anyone seen this before?

I’ve gone around the problem by not using lightbox popups in my directory. This works without problems in both IE and Firefox, but I thought I would document it and bring it to peoples attention.