javax.comm and tomcat5.5 problem

[Mitschu]

Hello
I want to send data strings via COM1 to a gsm Modem m20 (Siemens).
Sometimes it's by random I got the error:
java.io.exception: write error
at com.sun.comm.Win32SerialPort.write

Somehow if I flush the OutputStremWriter:
at java.iutputstreamWriter.flush(Unknown source)

Can someone help plaease?

Thanks
Michael