Nawel:

PS: I don’t have an Nvidia gpu so i didn’t install cuda


Unfortunately, you won’t be able to use mixed-precision training without a GPU.
The error message points towards an expected CUDATensor, while a CPUTensor was found.
That being said, once you get access to a GPU, we recommend to try out the native mixed-precision support from the current master branch or the nightly binaries as described here 4.