doubt regarding ethernet shield

recently i was purchased ethernet shield, when i connect ethernet shield with my arudino mega in my PC port is disappeared...ethernet shiled is unfitted condition with my mega port is appear...please give me good solution...

Hi - been running an Arduino fine with no shields attached. When I attached the Ethernet Shield and try to upload a sketch I get the output below.

I can upload the sketch without the shield attached and it's fine.

I'm using windows 7. Tried searching and I think the Ethernet shield might be using the serial ports differently. I'm very new to networking.

Help!!

Binary sketch size: 6958 bytes (of a 30720 byte maximum)

processing.app.SerialException: Serial port '/dev/tty.usbserial-A6008jGi' not found. Did you select the right one from the Tools > Serial Port menu?
at processing.app.Serial.(Serial.java:153)
at processing.app.Serial.(Serial.java:76)
at processing.app.debug.Uploader.flushSerialBuffer(Uploader.java:71)
at processing.app.debug.AvrdudeUploader.uploadViaBootloader(AvrdudeUploader.java:78)
at processing.app.debug.AvrdudeUploader.uploadUsingPreferences(AvrdudeUploader.java:53)
at processing.app.Sketch.upload(Sketch.java:1460)
at processing.app.Sketch.exportApplet(Sketch.java:1427)
at processing.app.Sketch.exportApplet(Sketch.java:1382)
at processing.app.Editor$45.run(Editor.java:2165)
at java.lang.Thread.run(Thread.java:613)
processing.app.debug.RunnerException: Serial port '/dev/tty.usbserial-A6008jGi' not found. Did you select the right one from the Tools > Serial Port menu?
at processing.app.debug.Uploader.flushSerialBuffer(Uploader.java:91)
at processing.app.debug.AvrdudeUploader.uploadViaBootloader(AvrdudeUploader.java:78)
at processing.app.debug.AvrdudeUploader.uploadUsingPreferences(AvrdudeUploader.java:53)
at processing.app.Sketch.upload(Sketch.java:1460)
at processing.app.Sketch.exportApplet(Sketch.java:1427)
at processing.app.Sketch.exportApplet(Sketch.java:1382)
at processing.app.Editor$45.run(Editor.java:2165)
at java.lang.Thread.run(Thread.java:613)
processing.app.debug.RunnerException: Serial port '/dev/tty.usbserial-A6008jGi' not found. Did you select the right one from the Tools > Serial Port menu?
at processing.app.debug.Uploader.flushSerialBuffer(Uploader.java:91)
at processing.app.debug.AvrdudeUploader.uploadViaBootloader(AvrdudeUploader.java:78)
at processing.app.debug.AvrdudeUploader.uploadUsingPreferences(AvrdudeUploader.java:53)
at processing.app.Sketch.upload(Sketch.java:1460)
at processing.app.Sketch.exportApplet(Sketch.java:1427)
at processing.app.Sketch.exportApplet(Sketch.java:1382)
at processing.app.Editor$45.run(Editor.java:2165)
at java.lang.Thread.run(Thread.java:613)