Can't invite people to party

[Lokisama]

For some reason i always get unable to invite when i try to invite people to my party, they can join my party just fine through the party finder but when ever i i try to invite them through for instance chat right click name and invite party says unable to invite

[Raist]

Is it an immediate message that you can't invite, or is there a delayed response? And what exactly is it saying?

Asking to rule out if it is because they are either rejecting the invite or simply not responding so it times out (some may do this to blind invites), or if perhaps they are already in a party or instance content or something that prevents them joining parties by design.