Hi Falco84,
PokerStrategy reserve the right to refuse membership as stated in the terms and conditions. It is usually where the member doesn't meet the criteria as laid out in the application for entry or fails the ID check etc, but can be one of a number of reasons.
They do not have to provide a reason and would never provide one to anyone other than the person applying themselves due to data protection reasons.
Your friend can ask customer support for further details should he/she wish, and would be able to do this themselves even with a deactivated account, however as stated above, detailed reasons are only given out at the discretion of customer support and they are not obliged to.
I hope this doesn't put you off of the TAF scheme which can be an excellent way to build up a bankroll and wish you well with your future referrals.
Best regards,
Bart