Been working on a Final Cut Pro project and had problems with dropped frames in playback. After clearing up room in ext drive the project still kept dropping frames. So I shut down the ext drive, closed all applications then ran Repair Disk Permissions in the Disk Utility in an effort to optimize my drive. Then went a step further and reset the NVRAM. Turned on ext drive and clicked on FCP project and got "Unable to Open Project File." This happens with other FCP projects on the same ext drive. I can open a FCP project on the iMac itself and it works fine. Please help!