I keep a Sparse Image on a password protected external HDD. It was created with computer A with FileFault turn on *not sure whether that matters) and the password to open the Sparse image is saved in the Keychain. Now on a different laptop, also running Sierra, the HDD does mount but the I can't open the Sparse image despite typing the password correctly. Someone *please* let me know how to fix this. The research I have done on Google points to the user's permissions. If I boot from my external backup for the first computer (cloned Macintosh HD) and mount that external HDD containing the Sparse image, it opens fine.