时间序列错误传递给参数&#39；的类型不受支持；数据&#39；

我有这个数据（时间是一个字符变量）：

problem = data.frame(time = c("2010-01", "2010-02", "2010-03", "2010-04", "2010-05", "2010-06", "2010-07", "2010-08", "2010-09", "2010-10", "2010-11", "2010-12"),
                     var = c(15, 16, 16, 14, 17, 12, 11, 15, 16, 18, 14, 11))


library(forecast)

fit <- auto.arima(problem$var)

pred <- forecast(fit, h=12, level=0.95)

我尝试制作时间序列图：

library(dygraphs)

dygraph(cbind(problem, pred$lower, pred$mean, pred$upper), main = "title") %>%
    dySeries("problem$var", label = "Actual") %>%
    dySeries(c("pred$lower", "pred$mean", "pred$upper"), label = "Predicted", fill = "red")

我收到错误：Unsupported type passed to argument 'data'.

我如何修复？