xrandr outputs errors when I try to add a new resolution

Question

I'm trying to add my own resolution, 1280x720 75Hz on my Nvidia card.

I've only come across this one method using xrandr, where you use cvt to get the parameters for your resolution and refresh rate, input it with xrandr --newmode, and then use xrandr --addmode to your display output. However, I get this error at the --newmode step:

$ sudo xrandr --newmode "1280x720_75.00"   95.75  1280 1360 1488 1696  720 723 728 755 -hsync +vsync
X Error of failed request:  BadName (named color or font does not exist)
Major opcode of failed request:  140 (RANDR)
Minor opcode of failed request:  16 (RRCreateMode)
Serial number of failed request:  53
Current serial number in output stream:  53

What's the problem and how can I fix it?