I dont have the luxury of 2 pcs with the game on ;p but i have logged into other characters on same account and had no probs with them so it is the actual ring that is causing the issue which makes it a game code error not a pc error i believe.
The actual ring code is obviously at fault and causing the block in my backpack untill it gets removed or recoded i will not be able to play on my main character.
It could be the config files for that specific character that have developed a fault, which
is your PC.
Go into your "Documents" folder and look for the "Runes of Magic" folder - you might need to turn on the Show Hidden Files option in Explorer.
Inside the "Runes of Magic" folder, delete/rename the folder of the specific character and try to log in to RoM.
It will re-create the folder with default settings and there's a possibility the ring might drop in properly.