Seems like this has been popping up a lot more lately. When dragging an app in the Applications folder, I'll get this "...info.plist is in use." After a number of tries, it will install. Just this morning, after 6 tries, it worked (with Cocktail). Mind you, none of these apps are running. Very annoying to say the least.

Have you restarted?

I got that constantly under Snow Leopard (10.6.8) and never did find a solution. Now that I'm in Lion, that particular annoyance is gone... but another one has popped up... having to authenticate to replace existing apps with updated ones (non-Mac App Store apps). Seems that in the years of migrating from one Mac to another, across operating system upgrades, etc., there are permissions issues that don't get fixed via Disk Utility.

One of these days I'm going to take the time to do this: Fix Finder Permissions Issue (http://reviews.cnet.com/8301-13727_7-57383188-263/what-to-do-when-the-os-x-finder-requires-passwords-for-managing-files/).

I restart or shutdown every other day or so.

I know. This post is dated. Now with mountain Lion, I find this nuisance. When dragging an app into the Apps folder, I will be asked if I want to replace or copy the App. I choose replace. Then, the progress bar continues as if it's doing it's thing. When it's almost done, then the authentication window pops up, I authenticate, and then the progress bar starts all over. I'm not booted into my Administrative account. Maybe it would behave differently if I was?