I've been using Time Machine to backup my MacBook Pro to my local OS X Server for years, but I recently started getting errors when attempting to backup. When running either an automatic or manual backup, I receive notification that the system couldn't complete the backup. After examining Console logs I'm seeing the following error from the NetAuthSysAgent process:

ERROR: AFP_OpenSession - Login failed with 80 

Additionally, the com.apple.backupd process is reporting an authentication error, and hints at System keychain problems:

Authentication error (80) - the correct user or password info may not exist in the System.keychain or the server may no longer allow access for this user.

I've confirmed that a keychain item exists in the System keychain for this connection, and that the keychain item should be functional (its type is Time Machine Password, it contains the correct password; Access Control for the item is always allowed for NetAuthSysAgent).

I've tried to remove the backup disk and re-add it through the TimeMachine System Preference. This seems to add the correct item into the System keychain, but the system still won't perform backup.

I've attempted to set the correct destination manually by performing the following command (trying the server's DNS name, IP address, and mDNS name without success):

sudo tmutil setdestination -p afp://USER@SERVER/TimeMachine

Each time that command runs, I can confirm that the correct Keychain Item is being created in the System keychain (but the system continues to provide the error mentioned above).

Lastly, manually connecting to the network share that hosts my Time Machine backup works normally, and my account has "Full Control" of files in this share.

How can I get my network Time Machine backups to work again?

up vote 2 down vote accepted

I found an answer on the Ars Technica forum, which helped to get the issue resolved: http://arstechnica.com/civis/viewtopic.php?t=1225417

The file at /Library/Preferences/com.apple.security.plist contained the following text:

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
   <key>DLDBSearchList</key>
   <array/>
   <key>SecItemSynchronizable</key>
   <true/>
</dict>
</plist>

It was necessary to remove the DLDBSearchList key and array from that file:

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
   <key>SecItemSynchronizable</key>
   <true/>
</dict>
</plist>

After removing that entry, Time Machine network backups are working normally (as NetAuthSysAgent is now able to locate the correct System keychain item).

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