Same problem for me.
* Ubuntu 10.10 32 bit, kernel 2.6.35-24
* USB adapter from EMTEC, ID 0bda:8172 Realtek Semiconductor Corp. RTL8191S WLAN Adapter
The solution of downloading a file from launcpadlibrarian.net suggested by logari81 worked like a charm! Thanks a lot!
BTW: you need to 'sudo mkdir /lib/firmware/RTL8192SU' before copying something inside ;-)