Unable to upload/verify anything to Printrboard/at90usb1286

Hello arduino world!

My friend gave me his 3D printer which is using a Printrboard/at90usb1286 control board. Everything is already built and wired up so i can connect the printer to Pronterface and move the axis', but what I would like to do is adjust the settings in marlin.ino and learn how to make modifications and all that jazz.

However, the only problem is that I'm unable to verify/upload anything to the control board. I've uploaded Teensy into arduino, and I've also replaced the boards.txt file in order for the correct boards to show up in the tools drop down menu. Still something is wrong. I'm receiving this error message:

Arduino: 1.8.10 (Windows 10), TD: 1.48, Board: "[BootloaderCDC]Teensylu/Printrboard"

Warning: Board teensy:avr:avr1091286 doesn't define a 'build.board' preference. Auto-set to: AVR_AVR1091286
Warning: Board teensy:avr:teensypp2 doesn't define a 'build.board' preference. Auto-set to: AVR_TEENSYPP2
Warning: Board teensy:avr:teensypp1 doesn't define a 'build.board' preference. Auto-set to: AVR_TEENSYPP1
Warning: Board teensy:avr:usbtiny1286 doesn't define a 'build.board' preference. Auto-set to: AVR_USBTINY1286
Warning: Board teensy:avr:utteensylu doesn't define a 'build.board' preference. Auto-set to: AVR_UTTEENSYLU
Warning: Board teensy:avr:cdcteensylu doesn't define a 'build.board' preference. Auto-set to: AVR_CDCTEENSYLU
Warning: Board teensy:avr:teensy1 doesn't define a 'build.board' preference. Auto-set to: AVR_TEENSY1
Warning: Board teensy:avr:teensy2 doesn't define a 'build.board' preference. Auto-set to: AVR_TEENSY2
exec: "C:\Program Files (x86)\Arduino\hardware\teensy/../tools/": file does not exist
Error compiling for board [BootloaderCDC]Teensylu/Printrboard.

This report would have more information with
"Show verbose output during compilation"
option enabled in File -> Preferences.

If anyone has any tips on how to solve this, or a better way to access this printrboard, it would be greatly appreciated.

I've attached a snip of the error message if need be.

Thanks for all your help

You installed the teensy core incorrectly (maybe following instructions for an ancient version of the teensy core and arduino IDE 1.0.x?).