I am running BOINC ver 7.16.11 (x64) under Windows 10. It has been many years since I attempted to add a new project but, as I recall, it always went without a hitch.

Recently, however, I have been trying to add GPUGrid.Net but, for a couple of days, my BOINC manager keeps returning the same message "Failed to add project. Please try again later".

The Event Log reports:

03/10/2021 11:28:56 | | Fetching configuration file from https://www.gpugrid.net/get_project_config.php
03/10/2021 11:28:58 | | Project communication failed: attempting access to reference site
03/10/2021 11:29:01 | | Internet access OK - project servers may be temporarily down.

However, the server status on the GPUGrid website seems to indicate that all the servers are running fine.

Any help would be welcome. Thank you.

It's a known problem, since about Thursday afternoon. GPUGrid is one of several projects affected.

See the sticky thread HTTP error: Peer certificate cannot be authenticated... at the top of this message board.

Thanks Richard, that is helpful.

This issue can be resolved by downloading the latest CA bundle from https://curl.se/docs/caextract.html. Copy and paste the downloaded pem file to <BOINC Installation Directory>/BOINC. Rename the pem file to ca-bundle.crt to replace the existing CA bundle.
You can keep the old CA bundle by renaming it to ca-bundle_old.crt first if you don't want to overwrite the existing one.

That should solve the issue and allow the BOINC client to connect to GPUGrid.