I thought I remembered seeing a thread like this here a while ago but couldn't find it.

Giving Premiere Pro a test drive and am using some footage I worked on in FCP X to do it. Simple import and very simple cut in PP. When I returned to FCP X the file showed up in the event manager in red with a dialogue indicating that my media file has been altered (or something like that)

I've got a project coming up that I'm going to have to finish in Premiere Pro (sharing the project with someone that only has PP). I want to do the rough cut in FCP X and then port out the XML to FCP 7 so that I can then kick it over to Premiere Pro. (whew)

Do I need to have two copies of the media that I want to cut with? One for FCP X and one for Premiere Pro?

Here's some info that describes your issue. It's an older post but my guess is there is still an incompatibility somewhere.

forums.creativecow.net/thread/335/13900

Don't know about PP but in AE prefs there is a setting to alter the metadata. You have to switch this off in AE. If you don't the media will go offline in FCP.

Ah, this is news I can use. I'll do some digging in PP to see whether or not its alterable. Thanks!