The above command you asked me to try didn't work:
snmpwalk -v 3 -u snmprouser -l authNoPriv -a MD5 -A snmpgdi 123 192.168.13.20
But the following worked:
snmpwalk -v3 -u snmprouser -l AuthPriv -a md5 -A snmpgdi123 -x des -X snmpgdi123 192.168.13.20
..and then I tried the plugin and that worked as well!:
/usr/local/nagios/libexec/check_ifoperstatnag 10101 -v 3 -u snmprouser -A snmpgdi123 -x DES -X snmpgdi123 -a MD5 -l AuthPriv 192.168.13.20
OK - Interface 10101 is up.
I guess that solves my issue for now, but I will try to investigate why the wizard wasn't generating the right command and will post here.
I know that this thread is quite old, but I ran into this same issue. It turns out that my passwords were too short.
Passwords as per RFC 2574 https://www.ietf.org/rfc/rfc2574.txt
Page 70
11.2 Defining Users
Paragraph 2
Requires that all SNMPv3 passwords be at least 8 characters long.
I made my two passwords longer than 8 characters and it fixed my problem.
Maybe someone else can find this useful.