After running Time Machine smoothly for a while, users may run into a problem wherein Time Machine will not back up anymore and will give an "Error -43" message.
Apple Discussions poster plarsen111 writes:
"I get a -43 error when starting Time Machine. Is there a way to fix this? I tried looking for updates, but no luck there."
The "Error -43" is a "File Not Found" error, which pertains to files, folders, and enclosing items such as disks or storage devices. This basically means that Time Machine cannot locate the Time Machine drive, which can possibly occur if either the Time Machine preferences files get corrupted, or if the hardware configuration changes such that the drive is being recognized with a different device label.
The following fixes may help users experiencing this problem:
Reselect the TM drive Users can go to the Time Machine system preferences and select the backup drive again. It may help to first remove the backup drive so there is none selected and also turn Time Machine off. Then turn it back on and re-select the backup drive, which should refresh the TM settings to properly point to the drive.
Remove the TM preferences If the Time Machine preferences file is corrupted, Time Machine may not be able to locate the drive. Additionally, users may not be able to properly set the drive in the system preferences, so removing the TM preferences may help clear the problem. The preferences are called "com.apple.TimeMachine.plist" and are stored in the /Macintosh HD/Library/Preferences/ folder.
Repair or Format Time Machine The TM drive contains many hidden files that are accessed by TM to pair up the drive with a given computer, and if these files are not accessible then TM will not work properly. Additionally, disk problems may prevent Time Machine from being accessed, it is recommended to run a "Disk Repair" routine on the drive using "Disk Utility" or supported third-party disk tool such as the latest versions of "TechTool", "DiskWarrior", or "Drive Genius". If the disk repair doesnt work, or doesnt find any problems, and the other mentioned fixes do not help, then users can try formatting their TM drive. This can be done with Disk Utility, and it is recommended to partition the drive so the partition tables are re-written. The specific format and partition type doesnt matter, since Time Machine will automatically reformat and partition the drive properly upon reselecting it. However, to do this with Disk Utility, users should ensure the drive is given a "GUID" partition scheme and is formatted to "Mac OS Extended (Journaled)".