SOLVED: MBP + High Sierra = Broken updates

[b0redom]

Hi All,
I have a 15" 2016 MBP running OSX 10.13. For some reason whenever I attempt to do an update I get:

"We could not complete your update. Unknown Error"

Triggering it from the command line using

softwareupdate -l

gives the following errors in the /private/var/log/install.log file:

Adding client SUUpdateServiceClient pid=4745, uid=0, installAuth=NO rights=(), transactions=0 (/usr/sbin/softwareupdate)
softwareupdated[420]: SUScan: Scan for client pid 420 (/System/Library/CoreServices/Software Update.app/Contents/Resources/softwareupdated)
softwareupdated[420]: Got status 200
softwareupdated[420]: Could not write catalog to /var/folders/zz/zyxvpxvq6csfxvn_n00000s0000068/C/softwareupdated/com.apple.SoftwareUpdate.SUCatalogDataManager/SUCatalog: Error Domain=NSCocoaErrorDomain Code=513 "You don’t have permission to save the file “SUCatalog” in the folder “com.apple.SoftwareUpdate.SUCatalogDataManager”." UserInfo={NSFilePath=/var/folders/zz/zyxvpxvq6csfxvn_n00000s0000068/C/softwareupdated/com.apple.SoftwareUpdate.SUCatalogDataManager/SUCatalog, NSUnderlyingError=0x7f88eae52d10 {Error Domain=NSPOSIXErrorDomain Code=13 "Permission denied"}}
softwareupdated[420]: SUScan: Elapsed scan time = 0.6
softwareupdated[420]: SUScan: Error encountered in scan: Error Domain=SUErrorDomain Code=106 "Can’t load data from the Apple Software Update server." UserInfo={NSLocalizedDescription=Can’t load data from the Apple Software Update server.}
softwareupdated[420]: Scan got error Can’t load data from the Apple Software Update server.
softwareupdated[420]: Removing client SUUpdateServiceClient pid=4745, uid=0, installAuth=NO rights=(), transactions=0 (/usr/sbin/softwareupdate)

I've not messed with any permissions... Anyone have any ideas?

 

[b0redom]

Solved, and the answer for posterity is.....

https://discussions.apple.com/message/33061884#message33061884