There are numerous examples of cryptic error messages which are hard or even impossible to get a meaning out of, I encountered one such error while trying to book train tickets using Indian Railways online ticketing facility provided by irctc.co.in. The error message was "The Dates given were outside ARP", while not too cryptic the message was also not very much self-explanatory and leaves no clues on what ARP means here???

A bit of digging got me my answer, the message meant to say that the chosen date for advance ticket booking was outside the allowed Advanced Reservation Period (ARP) allowed by Indian Railways. IRCTC allows you to book train ticket upto 60 days in advance and shows the above error when that is not the case, it is also to be noted that while the "date-picker" widget on the IRCTC site will allow you to choose the date within it's allowed range calculation of two months (which might include months having 31 days) the back-end system rejects the selection if the period is longer then 60 days.