I'm running Sabayon 3.4 and I configured ndiswrapper via the command line, to the point where everything works perfectly. However, I have to modprobe ndiswrapper every time I boot in order to get my wireless card working. I know this can be remedied with ndiswrapper -m, but doing so only gives me the error message in the thread title.

iwconfig looks like this:

wlan0 IEEE 802.11g ESSIDff/any
Mode:Managed Channel:0 Access Point: Not-Associated
Bit Rate:1 Mb/s Sensitivity=-200 dBm
RTS thr=2346 B Fragment thr=2346 B
Encryption keyff
Power Managementff
Link Quality:0 Signal level:0 Noise level:0
Rx invalid nwid:0 Rx invalid crypt:0 Rx invalid frag:0
Tx excessive retries:0 Invalid misc:0 Missed beacon:0

ndiswrapper -m is supposed to a write a file titled "ndiswrapper" to my /etc/modprobe.d directory, but of course there is none there.

Try manually check for/add a line entry like: alias wlan0 ndiswrapper