If you already tried holding down the Control & Shift keys to open the file after receiving a checksum error and the file still didn’t open, there’s not much that can be done. A checksum error basically means we are not getting the same information we wrote when the file was saved. Checksums are intended to detect data integrity problems, which can occur during file transfer or retrieval. I would use a hard disk utility and check the drive for errors. If the file was saved to more than one location, it’s not likely the copy would be affected.