Hi,

No.  The partition has enough space left:

/dev/ad10s2    256G    33G   203G    14%    /build

Manual fsck did not help.  I did it several times before and now again.
Sadly the machine crashed again last night.  And again no coredump:

dev = #ad/0x1e130057, block = 30408, fs = /build
panic: ffs_blkfree: freeing free block
mp_lock = 00000000; cpuid = 0
boot() called on cpu#0

syncing disks... Warning: vfsync_bp skipping dirty buffer 0xc4491550
640 Warning: vfsync_bp skipping dirty buffer 0xc4491550
619 Warning: vfsync_bp skipping dirty buffer 0xc4491550
[...]

Regards

	Matthias