******************* This email originates from outside Imperial. Do not click on links and attachments unless you recognise the sender. If you trust the sender, add them to your safe senders list https://spam.ic.ac.uk/SpamConsole/Senders.aspx to disable email stamping for this address. ******************* Dear Nektar: I want to install Nektar++ on Win10-WSL: Ubuntu 18.04 using the pre-compiled packages, but I encountered a problem. After Code: sudo apt-get update I get the following: Get:2 http://security.ubuntu.com/ubuntu bionic-security InRelease [88.7 kB] Hit:3 http://archive.ubuntu.com/ubuntu bionic InRelease Get:4 http://archive.ubuntu.com/ubuntu bionic-updates InRelease [88.7 kB] Get:1 https://www.nektar.info/ubuntu-bionic bionic InRelease [6114 B] Get:5 http://archive.ubuntu.com/ubuntu bionic-backports InRelease [74.6 kB] Err:1 https://www.nektar.info/ubuntu-bionic bionic InRelease The following signatures couldn't be verified because the public key is not available: NO_PUBKEY DB5E71FF7AC99B37 Reading package lists... Done W: GPG error: https://www.nektar.info/ubuntu-bionic bionic InRelease: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY DB5E71FF7AC99B37 E: The repository 'http://www.nektar.info/ubuntu-bionic bionic InRelease' is not signed. N: Updating from such a repository can't be done securely, and is therefore disabled by default. N: See apt-secure(8) manpage for repository creation and user configuration details. I have tried the following: Using different servers such as the following: code: curl -sL http://keyserver.ubuntu.com/pks/lookup?op=get&search=0xDB5E71FF7AC99B37 | sudo apt-key add gpg --keyserver hkp://keyserver.ubuntu.com:80 --recv DB5E71FF7AC99B37 curl -sL "https://keyserver.ubuntu.com/pks/lookup?op=get&search=0xDB5E71FF7AC99B37" | sudo apt-key add sudo apt-key adv --keyserver keyserver.ubuntu.com --recv-keys DB5E71FF7AC99B37 sudo apt-key adv --hkp://keys.gnupg.net--recv-keys DB5E71FF7AC99B37 gpg --keyserver hkp://pgpkeys.mit.edu --recv DB5E71FF7AC99B37 But, no good results.The key could not be found.Examples are listed below: Executing: /tmp/apt-key-gpghome.IoDko6URV5/gpg.1.sh --keyserver keyserver.ubuntu.com --recv-keys DB5E71FF7AC99B37 gpg: keyserver receive failed: No data gpg: no valid OpenPGP data found. Have tried to see if key exists with command: code: apt-key list but it is not listed there. /etc/apt/trusted.gpg.d/ubuntu-keyring-2012-archive.gpg ------------------------------------------------------ pub rsa4096 2012-05-11 [SC] 790B C727 7767 219C 42C8 6F93 3B4F E6AC C0B2 1F32 uid [ unknown] Ubuntu Archive Automatic Signing Key (2012) <ftpmaster@ubuntu.com> /etc/apt/trusted.gpg.d/ubuntu-keyring-2012-cdimage.gpg ------------------------------------------------------ pub rsa4096 2012-05-11 [SC] 8439 38DF 228D 22F7 B374 2BC0 D94A A3F0 EFE2 1092 uid [ unknown] Ubuntu CD Image Automatic Signing Key (2012) <cdimage@ubuntu.com> /etc/apt/trusted.gpg.d/ubuntu-keyring-2018-archive.gpg ------------------------------------------------------ pub rsa4096 2018-09-17 [SC] F6EC B376 2474 EDA9 D21B 7022 8719 20D1 991B C93C uid [ unknown] Ubuntu Archive Automatic Signing Key (2018) <ftpmaster@ubuntu.com> Regards, Xiangjun x_j_shan@outlook.com As you can see, many avenues explored with no good results. Looking for some help, please