When I logged in to My Accounts to transfer crowns, it showed my accounts with their current balance of crowns.
I just noticed today the last column said "non-transferable crowns". I'm not sure if that column was always there (didn't notice it before). Why would crowns be "non-transferable"?
Note: I "was" logged on to my "main" account. So I was able to make the transfer that I wanted. Just as an example, this one account had a total of 5075 crowns, and the "non-transferable" crowns were 75. Not sure why I wouldn't be able to transfer them.
Each account starts with 75 Crowns. Those Crowns cannot be transferred between accounts to prevent players from creating copious amounts of fake accounts and transferring the Crowns to a main account.
All purchased Crowns can be transferred between accounts, but usually Crowns given through promotions or contests cannot be transferred.