Error message: "connect: Invalid argument"
Kernel doesn't know, which physical or virtual link you want to use to send such ICMPv6 packets. Therefore it displays this error message.
Solution: Specify interface like: "ping6 -I eth0 fe80::2e0:18ff:fe90:9205", see also program ping6 usage.
Error message: "icmp socket: Operation not permitted"
This utilities create special ICMPv6 packets and send them out. This is done by using raw sockets in the kernel. But raw sockets can only be used by the "root" user. Therefore normal users get such error message.
Solution: If it's really needed that all users should be able to use this utilites, you can add the "suid" bit using "chmod u+s /path/to/program", see also program ping6 usage. If not all users should be able to, you can change the group of the program to e.g. "wheel", add this power users to this group and remove the execution bit for other users using "chmod o-rwx /path/to/program". Or configure "sudo" for fullfilling your security policy.