Well, I was traveling with Deekin and Valen, then made the Shield Guardian. Now I met the Scrivener in chapter 3. But the message says you can only have 3 henchmen at a time and Scrivener did not follow my PC. So, I talked to Valen and removed him from the party. That made me travel with Scrivener and I could complete his quest.
Now, my party is composed of my PC, Deekin, and the Shield Guardian. But the problem is, I cannot re-invite Valen to my party as the Shield Guardian is still counted as a henchman.
Is there any way to include Valen (or another character) into my party? Can I, somehow remove the Shield Guardian temporally from my party?
##Edit : Never mind. Using radial menu outside the gatehouse worked.