Lpc2000

I'm experiencing a weird phenomenon. I have THRE and RX interrupts
going on in the IAR compiler. After some very busy activity, all of a
sudden the TX pin gets stuck at low (mark). The weird thing is I have
3 boards sitting on the same serial bus and all of them do it at the
same time. It stays this way till reset. Nothing happens even if I try
to fill up the transmit buffer. It could be a problem on my board I
would have to look further but anyone have any suggestions?

Thanks