Error when I try to find themes or plugins inside the Dashboard

I have this error when I try to search for themes inside the admin area or to search for plugins. I don’t know why.

An unexpected error occurred. Something may be wrong with www.remarpro.com or this server’s configuration. If you continue to have problems, please try the support forums. How can I solve this problem forever? Tt annoys me and all owners of websites which have this common strange problem.