Thank you for pointing me to this library. Unfortunatley it produced similar errors.
As I am working on a commercial project I have been required to get a solution working quickly, so in the end I have taken the orignial library and translated line by line into a new one, elminating errors as they occured.
I have uploaded the new library to github. This is now tested and working in a RPi Pico. I hope it's of use to anyone else who needs to use the TLC59108 with the RP2040.
Cheers,