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If there is a dispute on hosting or domains charges some companies could slow this transfer down, until the outstanding balance is paid, check your TOC.
Or in some cases block your dns service on thier server.to prevent the dns change or domain transfer
If you give brief outline on question, maybe we can help
bennyandthejets, a DNS zone transfer has nothing to do with a domain's registration. But yes, a zone transfer can be blocked as well.