If the e-mail address of the current administrative contact for the domain is invalid, registrant won't receive the confirmation e-mail and won't be able to confirm the transfer.

The losing registrar can deny a transfer for several reasons:

• Evidence of fraud;
• UDRP Action
• Count order by court of competent jurisdiction
• Reasonable dispute over the identity of the Registrant or Administrative Contact
• No payment for previous registration period (including credit card charge-backs) if the domain name is past its expiration date or for previous or current registration periods if the domain name has not yet expired.
• Express written objection to the transfer from the Transfer contact.
• A domain name was already in “Lock” status.
• A domain name is in the first 60 days of an initial registration period.
• A domain name is within 60 days after being transferred.