Hi,
I have a Mega 2560 and when ever I try to download a file it says "serial port 'COM3' not found". Whats my problem I have the right board selected and I think the right programmer.
Thanks
1001100111100
What operating system type and version?
Windows 7 home premium, 64 bit.
Thanks for the reply 
1001100111100
I also have these problems with Win7 x64. I have to actually restart my computer for it to recognize it again...
I'm having the same issues with win7/x64, but for me it works just unplugging and plugging back in.
Happens every other time I plug the Arduino in. (Arduino Uno)
Yayaya it is working
actually it seems to vary with what USB port i'm using how often this occurs.