I'm having the same problem as you are, both steam and non-steam account have only one character, so that shouldn't be a problem, my steam connection is pretty stable, and I've been trying this for the past few hours, I'm not sure if I may have to restart steam, and I'll try that as I post this, so I'll edit the post if I find the solution or not.
Edit: Refreshed steam, took down the guard, even tried it in another computer (I have Steam and the games under an external HDD), apparently these are the causes:
a) You already linked a Non-steam account to your steam account (apparently there's a limit to one link per account).
b) All Knight slots are full.
c) Steam's own damn fault.
Either way, this is bothersome. I'm going to see if the SK staff could do something about this, if possible.
I'm having the same problem as you are, both steam and non-steam account have only one character, so that shouldn't be a problem, my steam connection is pretty stable, and I've been trying this for the past few hours, I'm not sure if I may have to restart steam, and I'll try that as I post this, so I'll edit the post if I find the solution or not.
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Edit: Refreshed steam, took down the guard, even tried it in another computer (I have Steam and the games under an external HDD), apparently these are the causes:
a) You already linked a Non-steam account to your steam account (apparently there's a limit to one link per account).
b) All Knight slots are full.
c) Steam's own damn fault.
Either way, this is bothersome. I'm going to see if the SK staff could do something about this, if possible.