I have a simple application, which should send a single byte to a serial port once a minute. But sometimes, from some strange reason, it freezes somewhere in the WriteFile() function. Both sw and hw flow controls are turned off. I've googled some stuff about pending read operations performed from another threads, but I believe this is not a problem, because my app has single thread. Also, handle from CreateFile looks valid, so the port should not be used by any other applications. Have anybody suffered this?