Final Cut Pro Share Fail

Final Cut Pro share fail occurs when exporting a one minute video to disc, but not with other share settings, such as Facebook & YouTube, Apple Devices. The reason given is a "Fail at Frame 361." However, it previously had given a different frame number for the fail point. Also, I tried to export a FCP video of the same length that had previously exported with no problem and now it is also failing with the same pattern as the new one. I am using an older iMac with 16gb memory and the files are on an external SSD drive. Thanks for any help!