Is "malformed base path in GetVolumeEntry" a cause of concern for Time Machine failing to start backing up? I have one Mac that sits at calculating changes and won't start copying files to the backup drive. Both the Mac and the external drive pass Disk Utility checks (repair / verify of the drive and the volume) and this machine has been happily backing up since February every few weeks when the drive is connected. This drive also has worked to back up two other Macs from time to time (both of which completed a backup with no issues three days ago).

Here is the message that gets logged when the Time Machine UI says "Calculating Changes"

com.apple.backupd[585]: malformed base path in GetVolumeEntry 


The tmutil status simply shows -1 for the Percent and I expect a NumberOfDeepScannedItems to count up as the changes are "calculated".

Does anyone know if this "malformed base path" is an actual problem or can be disregarded as something not necessarily causing this issue?
I was unable to determine why the malformed base path in GetVolumeEntry is being logged, but I can confirm that it wasn't the cause of the hung backup where Time Machine was endlessly "Calculating Changes".

I stopped the backup in process and then used Finder to navigate to the folder where Time Machine stores the backups for this Mac.

Moving the 2012-08-24-032413.inProgress package to the trash allowed Time Machine to work properly (i.e. start backing up in less than 5 minutes, completing the backup in under 10 minutes). The odd message about the malformed base path remains something that gets logged at the start of each backup attempt, but it's not something that prevents a backup from being saved. 

In this case I cared more about a prompt backup than why the partial backup was causing the current one to take so long.