The .hu TLD registry has special requirements for domains before nameservers can be changed. Please set up the e-mail address postmaster@yourdomain.hu or remove all MX records from the domain www.yourdomain.hu as long as the nameservers are being changed. First, You just have to create the postmaster@yourdomain.hu email, then your registrar will let you change the nameservers, otherwise, they will not let you do that.