Solaris Serial Port Locks Up

I open up a serial port asynchronously for reading and writing on a sparc ultra 60 running solaris 7. It will send messages properly for sometime and then after a while I can no longer send messages without rebooting the machine. The port is opened using open and ioctl. I was wondering if someone has run into this problem before. Was it not coded properly?, if so what’s missing that might account for such a problem. If not, then is there a way to flush it so I can continue to write to it?