Java APIs

I've put together a piece of code that is used to talk to a credit board/coin validator hooked to my PC via a serial port (comm 1).

My problem is that I receive a really strange error (IndexOutOfBoundsException) that occurs only between 17th and 20th of June. If i forward the system clock to a time and date earlier or later than this date range everything works as expected?

The error outputted is: java.lang.IndexOutOfBoundsException: Index: 6144, Size: 0

Any help on this would be real plus?....

Adam