First backup your family file by clicking on File > Backup Family File.
Using Windows Explorer, navigate to the Documents>Legacy Family Tree>_AppData>Temp folder and make sure all files are deleted from it.
Then try the process again.
If that does not work, then delete family file by clicking on File > Delete Family File. Next restore your family file from the backup copy by clicking on File > Restore Family File. When restoring, give your family file a different name that it previously had.
Click Here for detailed backup and restore guidance with helpful screen shots.