I recommend that you call Oregon Department of Revenue and explain your situation. If there's an error, they'll correct it.
They see some type of Oregon-source income and want the tax for it. If the letter doesn't give you any details as to what the taxes are for, the agent will have more information.
I'm enclosing a link for Oregon Department of Revenue contact information:
http://www.oregon.gov/DOR/contact/Pages/default.aspx
