sendnto problem?

hi everybody
I develop RTOS under Windows. After JTAG, I sent my OS image using sendnto. It works fine. The problem is after sendnto, I can’t reconnect to the develop board using the same serial port.
I use HyperTerminal under Windows. It says can’t open COM1.
Anyone has any ideas?

A windoze proggie complaining about a windoze device … I think you’ll find that only one proggie can use the comport at a time.

the most impossible problem is when sendnto exit, it didn’t close the serial port, but i don’t have the source code of sendnto, that’s why I ask.
maybe someone who know sendnto very well can explain