Sorry about that. My coworker is using a MacBook with OS 10.6.8 and InDesign CS5.5. She has a document open when trying to use the export command. She also has K4 installed on her machine, but was not logged into any servers.
K4 has the ability to control a lot of what a user can and can't do in a document. I don't remember whether Export was one of the items it could control, and I know there's a new version (or two) of K4 since I last used it.
But here's a simple test. Have her check the document back in or undo the checkout if she hasn't made any changes. Check it out on your computer. Does the Export option show for you? Now undo the checkout. Go back to her computer, log her out of K4, and log in on her computer using your log-in. Check out the document. If Export shows for you on her machine, but not for her, odds are something needs to be fixed in her user account, and you'll need to contact your K4 administrator to do that.
If it doesn't work under either account, it's probably an issue with that specific machine, and I'd check that you have the same plug-ins turned on and off, and that you have the same versions of the K4 plug-ins.