Unfortunately I spoke too soon. It appears the error is caused by 0 bytes free on the drive which is caused by a flooding of the flashphoner.log with these kinds of entries:
12:35:57,014 WARN StunUdpSocket - STUN-UDP-pool-43-thread-208 [id: 0x43a9e0a1, /172.31.12.52:31986] Failed to...