Help -Stuck with Find The Key

[CRBG]

Dylan the guard will not unlock the gate or give me a key to the castle. Everything I have read states all I need is King Mersent's letter, which I have. Am I missing something else, do i have to do something beforehand, or if it's bugged is the gate actually unlockable if I buff my lockpicking skill?

[Catacomber]

You need to have Merlin's Instructions in your backpack. Then he'll give you the key. But I don't remember where you get that.

I'll try to do an update but I don't know when Elendil will be able to get to it.