Computer can't find serial port

Hi, every time I try to upload my project to my Uno, the board says

Serial port /dev/cu.usbmodel411 not found

and asks me if I want to try another serial port, which all involve bluetooth. Occasionally, I'd get lucky and the correct serial port would show up after I randomly reset my board and plugged/unplugged the USB cable connecting my laptop to my board, but I'd like to know what's actually going on and how I can fix it permanently. Like I said before, I'm using the Uno, and my laptop is running Mac OS X Version 10.5.8. Thanks in advanced for all the help :smiley:

theere can be several reasons why this is happedning including that maybe your USB female sockets on the computer have gone loose(I experience it now they are loose due to wear and tear) or some other software is messing with serial ports on your computer.