ESXi 5 and The ramdisk 'root' is full

Hi,

I'm new to ESXi and have recently installed version 5 onto a server. Everything seems to be working OK, but the "The ramdisk 'root' is full" message is appearing frequently and I don't know why.

We store all our VMs on a NAS leaving the local disk purely for the ESXi server.

The ramdisk 'root' is full.  As a result, the file /var
/log/ipmi/0/.sensor_threshold.raw could not be
written.
error
26/04/2012 01:10:13
localhost.SSG-140

This is just one example, there are a lot but mention different files that can't be written.

Space seems OK.

Filesystem   Size   Used Available Use% Mounted on
NFS          1.8T  93.2G      1.7T   5% /vmfs/volumes/VM_NAS
VMFS-5     131.8G 971.0M    130.8G   1% /vmfs/volumes/local_disk
vfat         4.0G  11.4M      4.0G   0% /vmfs/volumes/4f291fe9-1a755017-25db-00237da16c8c
vfat       249.7M 127.4M    122.3M  51% /vmfs/volumes/d3b88a7e-71755e09-586a-2610ee101e71
vfat       249.7M   8.0K    249.7M   0% /vmfs/volumes/8fe72d7f-abce1db1-539b-c6d47e9f8369
vfat       285.8M 176.2M    109.6M  62% /vmfs/volumes/4f291fe2-fb7e77ce-d9e1-00237da16c8c

Any ideas?