Can't upload sketch to Leonardo, 'ser_open()' error message

I get the following error message while uploading sketch to the Leonardo board.

avrdude: ser_open(): can't open device "\.\COM17": The system cannot find the file specified.

avrdude: ser_send(): write error: sorry no info avail

My Arduino Leonardo is connected to COM18 port. I have rightly selected Arduino Leonardo under 'Boards' and AVRISP mkII as the 'Programmer' Also selected the Serial port as COM18.

I also tried to upload the sketch by Pressing and Holding the Reset button and releasing it when the status shows 'Uploading. . .' but in that case I get the following error. Kindly help

Found programmer: Id = "B«J"; type =
Software Version = .; Hardware Version = .
avrdude: error: buffered memory access not supported. Maybe it isn't
a butterfly/AVR109 but a AVR910 device?

This issue is getting me frustrated. I tried every possible Troubleshooting..
Someone may please help me