I've had a similar problem. Actually I've forgotten to remove this line in my vsftpd.conf :
Yes, in the INSTALL file they say to write down this line in configuration file (for testing in standalone mode), but didn't say to remove it when using inetd; now I think it's obvious
Both Inetd and vsftpd were trying to listen on the same port, hence the error message.
Try to remove or comment out this line