Hi,
This just got me too. I have several of these running great with Raspberry Pis but just started a project using a Pro Mini and didnt want to write another library (which i normally like doing).
Look at your error output, i think there is a typo in the library:
In the TSL2561.cpp file, it is “byte writeUInt”
In the TSL2561.h file, it is “boolean writeUInt”
They need to match. I think they should both be “boolean” which seems to be consistent with the others.
b