as far as I remember, I only install sonnb-xengallery.
However, I have my friend setup as admin does not have problem with 'start conversation'
He can message me and other member can message me through start conversation... but fror some reason I do not have permission and get the error above.
Make sure that the number of participants is set higher than 0 in the registered (if you allow all registered users to do it) or higher than 1 in your Admin user group that you are a member of.
Depending on how you have implemented your user groups, odds are that you have something other than registered as your primary (if you already have it so that registered has more than 0 participants)... and you have your primary as something like Administrator which is set at 0 particpants.
You have it set as unlimited... so that should be working - unless you are a member of a group that has "never" set for conversations. If you want, you can start a convo with me with ACP access and I can take a quick look at it and see if I can figure it out. Shouldn't be anything that major.
Think I found the problem (one amongst several).
You had a secondary group membership for the user you sent me of Newly_registered. In that group you had this set
As you can see... you set Never... which over-rode all other settings. I removed you from that group and it should work now (further, I set the group to use the Not Set (No) setting).
Additionally, you did not have the account assigned with the normal Registered as primary and using the secondary for all other groups (which is something I mentioned in an earlier post). That also has been fixed for that account. You need to review @Brogan's most excellent resource on implementing permissions in XenForo then make adjustments to your current setup to work within the suggested guidelines.
No problem... was glad I could help. If that was your normal account you may want to change the password. I'll leave the conversation and once you leave it then neither one of us can see the one you gave me again.