I have an Arduino Uno R4 Minima, I'm trying to connect a mlx90615 IR sensor. I have downloaded the library for this sensor, when using there example to test the sensor I get this error. Exit status 1 unknown cpu. When trying the example code for the screen I got, everything works. Maybe the code isn't updated for the R4? I'm very new to the Arduino and codding so this may be an easy fix, hopefully.
You really should have included a link to the library that you're using.
If this is the library you're using, it's not going to be a quick fix. My first impression after looking at it: what a bass ackwards way of doing things!
Welcome to the forum
Many libraries have not yet been updated to be compatible with the Renesas processor used in the Uno R4 boards and it is possible than some will never be updated
Yes that is the corrext liburary i used. Whats your all best opinion to move foward. Buy an older board? Just trying to make a belt temp monitor.
If you don't have an overpowering need for some capability that only the R4 has, by all means buy an R3 and spare yourself much hair pulling. 
You can fork the library.
As far as I can see TwiMaster in I2cMaster.(h|cpp) is not used.
Remove the class and also remove TwiMap.h.