registration problem,

I sent my link to my friends. but they cannot register which says " There is a ip restriction. Which means it's not allowed in singapore." are singaporean members profited?
thanks a lot.

can't they make an account or they can't confirm their accounts?

they can not make an account.

Seems like they're connected to the same IP address you're on OR they clicked too many times on the "Register" link. If it's the first option they cannot register but if it's the 2nd ask them to do the following:

They need to disconnect their modem for 20 seconds, and reconnect it and then try to register again.