In fastserial/Msp430UartP.nc the UartStream.send function only works when the buffer has a length of 1 byte. This is a regression compared to chips/msp430/usart/MSP430UartP.n where UartStream.send supports a buffer of arbitrary length.
It looks like much of the chips/msp430/usart/MSP430UartP.nc could simply be used in fastserial/Msp430UartP.nc instead.