Error: Failed to serialize user into session

[jgaull]

I'm getting the error Error: Failed to serialize user into session when testing login functionality. If I set session to false then the error stops. The full stack trace of the error is:

Error: Failed to serialize user into session
    at pass (/Users/Jon/Code/Ryde/Server/node_modules/passport/lib/authenticator.js:271:19)
    at Authenticator.serializeUser (/Users/Jon/Code/Ryde/Server/node_modules/passport/lib/authenticator.js:289:5)
    at IncomingMessage.req.login.req.logIn (/Users/Jon/Code/Ryde/Server/node_modules/passport/lib/http/request.js:50:29)
    at Strategy.strategy.success (/Users/Jon/Code/Ryde/Server/node_modules/passport/lib/middleware/authenticate.js:235:13)
    at ParsePromise.success (/Users/Jon/Code/Ryde/Server/node_modules/passport-parse/lib/strategy.js:81:25)
    at ParsePromise.<anonymous> (/Users/Jon/Code/Ryde/Server/node_modules/parse/lib/node/ParsePromise.js:317:27)
    at ParsePromise.wrappedResolvedCallback (/Users/Jon/Code/Ryde/Server/node_modules/parse/lib/node/ParsePromise.js:153:43)
    at ParsePromise.value (/Users/Jon/Code/Ryde/Server/node_modules/parse/lib/node/ParsePromise.js:89:36)
    at ParsePromise.<anonymous> (/Users/Jon/Code/Ryde/Server/node_modules/parse/lib/node/ParsePromise.js:163:29)
    at ParsePromise.wrappedResolvedCallback (/Users/Jon/Code/Ryde/Server/node_modules/parse/lib/node/ParsePromise.js:153:43)
    at /Users/Jon/Code/Ryde/Server/node_modules/parse/lib/node/ParsePromise.js:219:35
    at _combinedTickCallback (internal/process/next_tick.js:67:7)
    at process._tickDomainCallback (internal/process/next_tick.js:122:9)

In index.js I have

app.use(cookieParser())
app.use(bodyParser.urlencoded({ extended: false }))
app.use(session({
  secret: 'a secret',
  resave: true,
  saveUninitialized: true,
  store: new ParseStore({
    client: Parse
  })
}));

var parseStrategy = new ParseStrategy({
  parseClient:Parse,
  appId: appId
})

passport.use(parseStrategy)

app.use(passport.initialize())
app.use(passport.session())

app.get('/login', site.loginForm)
app.post('/login', site.login)
app.get('/logout', site.logout)

app.get('/dialog/authorize', oauth2.authorization)
app.post('/dialog/authorize/decision', oauth2.decision)
app.post('/oauth/token', oauth2.token)

site.login looks like

exports.login = passport.authenticate('parse', {
	session: true,
	successRedirect: '/dialog/authorize/decision',
	failureRedirect: '/login'
})

I've googled around extensively and it looks like most people get this error when serializeUser is not defined. But I took a look and passport-parse definitely defines both a serializeUser and deserializeUser method.

Any help would be great. Please let me know if I need to post more information.

Thanks!