If you receive the error "Agent admitted failure to sign using the key" when trying to SSH into a remote machine, it typically means that the SSH agent on your local machine is unable to use your private key to authenticate the connection. This can be caused by a number of factors, including:
The private key is not stored in the default location (~/.ssh/id_rsa). In this case, you will need to specify the correct location using the -i option when connecting.
The private key is encrypted and you have not entered the correct passphrase. In this case, you will need to enter the correct passphrase when prompted.
The private key is not in the correct format. SSH supports several different key formats, including RSA and DSA. If you have generated your key in a different format, you may need to convert it to a supported format using a tool such as ssh-keygen.
There is a problem with the SSH agent on your local machine. This could be caused by a configuration issue or a problem with the agent itself. To troubleshoot this issue, you can try restarting the SSH agent by running the following command:
eval "$(ssh-agent -s)"
You can then add your private key to the agent using the following command:
ssh-add ~/.ssh/id_rsa
If the problem persists, you may want to check the log files on your local machine and the remote machine to see if there are any clues as to the cause of the problem.
Overall, the "Agent admitted failure to sign using the key" error can be caused by a variety of issues, but it is usually easy to resolve by specifying the correct private key location, entering the correct passphrase, or restarting the SSH agent.