An HTTP error occurred when trying to retrieve this URL. HTTP errors are often intermittent, and a simple retry will get you on your way.
when i click that link above,i see like this
I am having the same issue.
I downloaded qiime2-2017.11 natively through terminal and it worked fine, however when I try to update to qiime2017.12 in the same way I get the error message.
As suggested I tried
source deactivate qiime2-2017.11
conda env remove -n qiime2-2017.11
Before installing, then that didn’t work and I also tried