Time Machine BackUp Error Code 402

Unfortunately, this is one of many errors that will display when a Time Machine backup file has become corrupted. We see this occurring often with Macs that have been "upgraded" to the Catalina operating system.

Hold down the option key on your Mac while you click on the Time Machine "clock" icon at the top of the screen

Click on Verify Backups

It might take anywhere from 10-60 minutes or more for the process to complete, depending on how much data is stored on your Time Capsule's hard drive. Allow the process to run to completion or until you see another error message.

If you do see an error message, post back the exact text of the message.

You can check the progress of the Verify process by holding down the option key and clicking on the Time Machine "clock" icon.

Apple has never released a nice document outlining error codes and what they actually mean.. It may as well say..

Error .. guess a number.. any number.. multiply by your age, divide by the day of the month.. add 1-4 depending on the quarter the moon is in.. and the current wind speed.

BUT we are very familiar with errors involving Time Machine, Catalina and Time Capsules.

It is basically a recipe for pain and suffering.. add these 3 ingredients .. boil until dry and the flames burn a hole in the pot.. complain loudly to the universe.. and check out if AppleCare. (Hint.. they don't).

You need to remove one of the 3 ingredients.

Time Machine.. is very very unreliable with Catalina.. especially to Network devices.. and double especially to Time Capsule which does not support the main protocol, SMB2 or SMB3 now used by Apple.

Use a suitable substitute.. Carbon Copy Cloner is a good one.

Catalina. Well that is unlikely you are going to roll back to something prior but the temptation is there.

Time Capsule. Hmmm.. how old is your TC? Have you done a reset of it? Have you archived all the backups and erased the disk and started again. Catalina has loads of issues with TC.. but certainly to have any hope of reliable backup I would do the afore mentioned preparation. Certainly any TC that is older than 5 years should just be replaced. Between 3-5 years.. a full factory reset with short names, no spaces and pure alphanumerics can be given a go .. erase the drive after archive if you have backups you wish to keep.

Time Machine is much more reliable to target that supports SMB2 or SMB3 like Synology NAS. Or use a local USB drive.