There are various cases where a domain name may not be transferable to another Registrar. This could happen in the following circumstances:
Domain name is less than 60 days old: If the domain name you are trying to Transfer was registered less than 60 days ago, the request will get rejected by the Registry itself.
Domain name has been Transferred less than 60 days ago: A domain name can not be transferred to another Registrar within 60 days of a previous Transfer.
A domain name can not be transferred from Registrar B to Registrar C, if it has been transferred to Registrar B from Registrar A within the last 60 days.
Theft Protection / Lock / Suspension has been applied on your domain name: If Theft Protection / Lock / Suspension has been applied on your domain name at the Current Registrar, then a Transfer for that domain name to another Registrar will not be allowed. You will first have to disable Theft Protection / Lock / Suspension for the domain name and then proceed with a Transfer.
Privacy Protection has been enabled on your domain name: If you have enabled Privacy Protection for your domain name, then you need to disable it, before trying to transfer it.
Domain name is in the Redemption Grace Period or in the Pending Delete status: If the domain name is in either of these statuses, it can not be transferred.