aerender stops with error on a network

Hi,

I am setting up a small renderfarm. Now I have 3 render nodes and they read/write the project files from/to a Xsan server. The nodes have rights to read/write on the server but once I start the aerender in Terminal I get (apparently) random errors like these two:

aerender Error: After Effects error: opening resource file /Volumes/XsanServer/Render Files/Comp 1_00023.jpg

or

aerender Error: After Effects error: Can't set catalog info file /Volumes/XsanServer/Render Files/Comp 1_00023.jpg.

My first guess is that there were some kind of problems with the nodes trying to write the same file at the same but the first error pops even when I use only one of the render nodes alone.

Rendernodes are running OSX 10.6.8 and After Effects CS6.

Any clue where these errors come from or what they mean?