You could try to do the following:
Logout from the game!
Go to the folder where your addon's save data is stored, normally this should be something like
Code:
c:\users\<your windows login name/user name>\documents\Elder Scrolls Online\live(eu)\SavedVariables
Copy the whole folder to another place as as backup.
Afterwards search for the file MasterMerchant.lua or something like MM*.lua and delet/rename them.
Login again and try if it works now.