I can´t upload my sketch when i connect the ethernet shield

hello, I'm doing a proyect when I need to use the ethernet shield arduino connected to my arduino uno. When I verify my proyect it´s all ok, but when i try to upload with the ethernet shield connected to arduino sometimes say me that the serial port is not find and other sometimes appear me "Serial Port "COM X" already in use. Try quiting any programs that maybe using it.". I have been cheked this and if try to upload any example with serial port this work when i try to use ethernet shield i can´t =(. can say me Somebody if i can fix this or if the ethernet shield is dead u.u ???

try holding down your reset button before you click upload..

release the button when you see the compiler size message just before it uploads..

Saw it here somewhere and it has worked for me..