I had this problem since months and i don’t really remember where it actually started because i never gave it much attention but currently, i want to fix it although i have a lot of addons so i tried to set each of them off in a middle of a fight until i figured out who was the reason behind the problem. Unfortunately it was TSM addon…
Tried to use google to find a solution but nah. Tried to reinstall the addon but it also didn’t worked and i don’t want to disable/delete the addon as it helps me knowing the prices of the items i have 
So is there any solutions to this?
No, not until said addon is updated to work with the newer version of WoW.
May have to wait until there’s a new version of the addon out. Maybe see if the developer of said addon knows of the error so that it can be worked out.
That error occurs when the addon tries to call a protected function.
Addons try and call protected functions because the functions were once public functions, but Blizzard decided to disable that function, for various reasons. When that happens, either
- The addon breaks and remains broken and becomes deprecated.
- The addon gets recoded to work around the loss of whatever function call it was trying to make.
Basically, what Hoisho said, you gotta wait for the maintainers of that addon to update it, if an update is even possible.