php_serial.class.php problem

I am using the php_serial.class.php script to control an Arduino Duemilanove connected to /dev/ttyUSB0 on my local web server, and controlling it from another PC.

When I start the server the PWR LED light. Then if I try to send commands from the web browser the RX and the L LED's flick momentarily on the Arduino but there is no change of state to the LED's connected to the digital outs.

But if I start the Arduino IDE on the server and its 'Serial Monitor' I can the control the LED's on the digital outs from my web browser, the RX and now the TX (but not the L) LED's flicker and the data returned can be viewed in the 'Serial Monitor'.

If I then close the 'Serial Monitor' and the 'Arduino IDE' I can control the LED's from the web browser.

It seems to me the something is changed once the 'Serial Monitor' has been started. Has anybody else experienced this and what do I need to change. I have looked at many posts and tried some changes but none have overcome the problem?

The server is running Xubuntu 10.04 Kernel 2.6.32-29

Thanks in advance