The task bar reads: "zipping audio+G with zLib" followed by the song name.
I restarted holding the shift key and the error didn't pop up. So I started to rip a disk. And as soon as it tried to zip a new encode, I got the same error.
The first time this happened, I was prompted for a crash report, but failed to send it. I've gone ahead and generated one, hopefully it will have the correct information.
I was editing the meta data for rocky top at the time this first happened. i.e., it was not during a rip. And I was playing a song at the same time, but it wasn't rocky top.
For the record, the volume isn't locked, nor is the xattr file referenced (although the only one I can find for rocky top lacks the "KJ_Safe_Save " prefix shown in the error dialog) and there's plenty of space on the volume.
I have sent the crash log and console log via email with the above explanation.