If you change the value of your parameter [Months to Forecast] to 2 or less, you'll get a result back. Not an R expert, but that seems to be happening because you only have 3 months in your data set. For instance, if you try this calculation, it works:
time <- ts(.arg1, start=c(2014,1), frequency=12);
fcast <- forecast(time, h=.arg2);
append(.arg1[(.arg2+1):n],fcast$mean, after = n-.arg2)",
The attached workbook has an example with SuperStore in Tableau 10.
Insurance_ss.twbx 1.5 MB