hi from russian guys. I'm teaching english by the way
I think you have incorrect kernel configuration.
Type a command:
less /proc/config.gz | grep 2303
Correct result is :
CONFIG_USB_SERIAL_PL2303=m
or
CONFIG_USB_SERIAL_PL2303=y
Incorrect result is:
# CONFIG_USB_SERIAL_PL2303 is not set
If incorrect, you need to rebuild the kernel.
Best regards!
P.S. Have you search this site for keyword "pl2303"?