tcplay not working if XOrg running

[Uwe Münzberg]

why can I not map the encryptet volume?

probook# whoami
root
probook# dd if=/dev/zero of=secfile bs=1024k count=10
10+0 records in
10+0 records out
10485760 bytes transferred in 0.018927 secs (554007824 bytes/sec)
probook# vnconfig -c -v vn0 secfile
/dev/vn0: secfile, complete file mapped
probook# tcplay -c -d /dev/vn0
Passphrase: 
Repeat passphrase: 
Summary of actions:
 - Completely erase *EVERYTHING* on /dev/vn0
 - Create volume on /dev/vn0

 Are you sure you want to proceed? (y/n) y
Securely erasing the volume...
This process may take some time depending on the size of the volume
Creating volume headers...
Depending on your system, this process may take a few minutes as it uses true random data which might take a while to refill
Writing volume headers to disk...
All done!
probook# tcplay -i -d /dev/vn0
Passphrase: 
Device:                 /dev/vn0
PBKDF2 PRF:             RIPEMD160
PBKDF2 iterations:      2000
Cipher:                 AES-256-XTS
Key Length:             512 bits
CRC Key Data:           0x50bc6cb8
Sector size:            512
Volume size:            19968 sectors
IV offset:              256 sectors
Block offset:           256 sectors
probook# tcplay -m secdev -d /dev/vn0
Passphrase: 
libdm /usr/src/lib/libdm/dm_task.c:289: error: ioctl failed: 9
dm_task_run failed
Could not set up mapping secdev
probook# kldload md
kldload: can't load md: module already loaded or in kernel