Disableb communication over COM1 - strange behaviour

I have problem, when I start process which doesn't use serial port it disable all communication over COM1, but when I start app from another machine which communicate with this process it works. What could be problem ? Is seams like when I start 开发者_开发知识库Java on that machine it disable communication. Any idea ?

Well in order for a Java application to take over some COM port you need to use JavaComm. Are you using JavaComm in your app?