Soon after setting up my local site I started getting Cookie errors thrown in the form "Cookie names cannot contain any of the following '=,; \r
\013\014'" whilst trying to initiate the session.
In the Admin Plugin>Configuration I changed the session name from "grav-site" to "something else" and inadvertently introduced an error. This value is used to form the cookie name and Cookie names may not contain spaces. Only after quite a bit of investigation (coming from a non-coder) did I discover the cause. Well, I'm grateful that I found the error.
I think though that if someone inserts a space in the session name, that should be converted to some other character to avoid this error from being thrown.