[TTMT]

For people with "Your invite is either not valid or has already been used." error message:

Technical reason: the invitationcode field in the table invites in your database has length at most 20 characters, whereas the one being sent to users has 32 characters. What happens is usually the invitation token (with 32 chars) generated randomly will be sent to users (in the invitation link), although only the first 20 characters of this token is gonna be stored in the database. When users click on their link, the system basically lookup in the invites table to see if there is any match, but it clearly fails.

Solution:
1. If you have already installed the system, simply go to your invites table (using myphpadmin or any similar database management tool), and change the length of the invitationcode field in the invites table to 32. Notice that this invites table might have prefix (chosen by you at installtion), therefore just look for any table that ends with invites.

After that any new invitations should work. You can delete all previous records in the invites table if you wish.

2. If you haven't installed the system (or want to uninstall your system and reinstall it) then:

First, open product-invitation.xml and find

$db->query_write("CREATE TABLE ". TABLE_PREFIX ."invites (
  invitecode varchar(20) NOT NULL default '',

then change 20 to 32.

Then install the system as normal. It should work (tested on vbb 3.6.8 patch level 2).