Avoid 4.5.1.1456 QNAP Firmware Update
Besides causing issue with using Emby it has numerous other issues - which is very common these days from QNAP
Please avoid jumping on new firmware updates till they have a couple of weeks to be tested - especially if you a running critical apps on your NAS
and especially if you consider Emby to be critical to you.
See https://forum.qnap.com/viewtopic.php?f=142&t=157375 for some of the other issues people are facing.
Luke