Vsftpd
 

550 Directory create operation failed in fedora 12 while creating dircetory using ftp.

Does the account you've used to log into the ftp server has exec permission on that directory? IIRC you need exec permission to create directories.

Actually, x on a dir is search perm, you'll need w.
Have a read of the vsftpd docs http://vsftpd.beasts.org/vsftpd_conf.html