ERROR decrypt error: unable to find a PGP decryption key for this message

On one of my devices, I am unable to decrypt any PGP encrypted messages.

```
~ keybase --version
keybase version 1.0.15-20160404130015+8ac9934
```

```
~ keybase pgp decrypt -i /tmp/encrypted.asc
ERROR decrypt error: unable to find a PGP decryption key for this message
```

```
~ keybase pgp select --only-import
ERROR No PGP keys available to choose from.
```

So I tried exporting my PGP public & secret (private) key to gpg to see if that would help. Exporting the public key works fine.

But when I try to export the private key,

```
~ keybase pgp export -s
ERROR No matching keys found
```

What have I done wrong to get in this conundrum?

Start by reproducing the reported keybase pgp decrypt, pgp select --only-import, and pgp export -s commands using the provided outputs. No source file or test is identified; a useful result would first establish why the public key is available while no private decryption key is found, then identify the affected code or test.

Written by the indexing model from the issue text.