[PCMCIA] Ethernet Card seems to be busy

Hi.
I'm a beginner beginner with Linux (Debian 3.0), but I've much knowledge about Pc's.

So, I have a Sitecom Fast EthernetCard (Serial#: CB-001) for my PCMCIA-Slot here.
It uses a Realtek 8139 Chip, so it's no problem, to install 8139too.o.
Now I have my eth0-Interface, but I can't configurte it.
If I try to change the IP-Adress with "ifconfig eth0 192.168.1.1" or similar,
I get this message:
"SIOCSIFFLAG: Device or resource busy."

//*** Some Outputs, maybe you need them:

Output of CardMgr, when I plugin the card:
cb_alloc(bus 32): vendor 0x10ec, device 0x8139

Output of lspci:
20:00.0 Ethernet controller:
> Realtek Semiconductor Co., Ltd. RTL-8139 (rev 10)

Output of dmesg:
> PCI: Enabling bus mastering for device 20:00
> PCI: Increasing latency timer of device 20:00 to 64
> eth0: 8139too Fast Ethernet driver 0.9.18-pre4 Jeff Garzik <(E-Mail Removed)>
> eth0: Linux-2.2 bug reports to Jens David <(E-Mail Removed)>
> eth0: RealTek RTL8139 Fast Ethernet board found at 0xc4042000, IRQ 0
> eth0: Chip is 'RTL-8139C' - MAC address '00:10:60:5d:62:fb'.

Output of "ifconfig eth0":
> eth0 Link encap:Ethernet HWaddr 00:10:60:5D:62:FB
> BROADCAST MULTICAST MTU:1500 Metric:1
> RX packets:0 errors:0 dropped:0 overruns:0 frame:0
> TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
> collisions:0 txqueuelen:100
> RX bytes:0 (0.0 b) TX bytes:0 (0.0 b)
> Base address:0x2000

//**** End Outputs

HFH,
greetz Alexander Surma