+\H{errors-key-wrong-format} \q{Unable to use this private key file},
+\q{Couldn't load private key}, \q{Key is of wrong type}
+
+Various forms of this error are printed in the PuTTY window, or
+written to the PuTTY Event Log (see \k{using-eventlog}) when trying
+public-key authentication, or given by Pageant when trying to load a
+private key.
+
+If you see one of these messages, it often indicates that you've tried
+to load a key of an inappropriate type into PuTTY, Plink, PSCP, PSFTP,
+or Pageant.
+
+You may have specified a key that's inappropriate for the connection
+you're making. The SSH-1 and SSH-2 protocols require different private
+key formats, and a SSH-1 key can't be used for a SSH-2 connection (or
+vice versa).
+
+Alternatively, you may have tried to load an SSH-2 key in a \q{foreign}
+format (OpenSSH or \cw{ssh.com}) directly into one of the PuTTY tools,
+in which case you need to import it into PuTTY's native format
+(\c{*.PPK}) using PuTTYgen - see \k{puttygen-conversions}.
+