- unmount the volume from all the machines
- ssh into QNAP and change to the root folder of the volume (in my case /share/MD0_DATA/Qmultimedia )
- delete the folders below
.@__thumb/
.AppleDB/
.AppleDesktop
.AppleDouble/
:2eDS_Store
- mount the volume again and in my case I no longer get this annoying message (those folders deleted will be recreated again)
I've got this problem on the time machine volume where I found only 3 directories to delete
.AppleDB/
.AppleDesktop
.AppleDouble/
After this the Time Machine backup starts again without any warning! So 1 billion thanks to metro_monkey that solved (at least to me) the problem and 1 Billion ******* to Qnap support that gave non answer since August 2010!! Sahme on You!