Dear folks!

If BOINC on your computer experiencing a problem during project communicating, try to replace file ca-bundle.crt in programs directory of BOINC (C:\Program Files\BOINC\ca-bundle.crt, for example) by this file: https://srbase.my-firewall.org/sr5/download/ca-bundle.crt and restart whole BOINC processes or reboot computer.

Another threads on forum:
Peer certificate cannot be authenticated with given CA certificates
Wus not uploading
Transient Error
Communication deferred
100% block still crunching

Thank you for participation!

Source