Hi,
It’s very hard for me to help you with this error without any context code at all 
What I believe might be the issue is that tensor  in your case is a Tensor, while other_tensor is a Variable. For example, this code will fail with precisely this message:
auto x = at::ones(at::CPU(at::kFloat), {2, 2});
auto y = at::randn(torch::CPU(at::kFloat), {2, 2});
x.copy_(y);

where the first tensor is created with at::CPU type, which creates a tensor, while the second is created with torch::CPU type, which creates a variable. Could this be the error you ran into? In that case, please change the first to torch::CPU.
If not, please elaborate on your code so that I have a chance to better understand it.