"Sign into the iTunes store" keeps popping up
"Sign into the iTunes store" keeps popping up and no matter how many times I type in my correct password it just immediately pops up after. It will not let me quit the application and I need to do so in order to restart my computer for an update. I have tried to delete the application but it cannot delete while it is still open and it won't close or quit.
MacBook Air 13″, macOS 10.12