Since blizz changed some things about low pop realm and s@#t (dont realy know what exactly) inviteing people to a low pop realm is not posible.
I have 2 accounts on same battle net account
On my second account i have a 90 on a low pop realm with wich i was inviteing my B.1 account to farm and what not.
This night a friend of mine asked me to invite him and i was not able ... but he was
After some searching on bnet forums i found out that high pop realm now have priority on inviteing.
So wile trying to figure out a way how to inv from low pop a high pop realm i found this:
1. Log low pop char and inv high pop char
2. Send inv from High to Low and make Low one leader
3. Low one invites a nother player ( the one who needs to get ported) but hes not pressing accept
4. Low pop kick High pop => low pop gets ported back
5. Second High pop accepts
6. Profit !
Hope this works for others
Ps. Its late ... hope u get what i ment in all this