OpenKeychain complains about signing subkey despite a green icon

Expected behavior

I should be able to send PGP encrypted email.

Actual behavior

I can no longer send PGP encryped email.

The new version of K9 that uses OpenKeyChain is simply broken.

I've been using K9 + AGP for years, and it always worked 100%.

If it was possible to get it working, I should have been able to do so: I have been professionally programming for 20 years, and I understand how PGP ticks at a basic mathematical level. If I failed, how much chance would a beginner have?

Steps to reproduce

Note: these steps work 100% with K9 + the old APG (which is now deprecated).

1. Import my PGP public key into OpenAGP. I never import my private key, as I want to have one-way communications between my phone, and Outlook running on my PC.
2. Send email using K9 + OpenAGP.
3. K9 throw an error which prevents the email from getting sent:

Discussion

The error that K9 throws is not very helpful. It gives no real clue that would help solve the issue. I must admit - I'm stuck. I havn't been able to send an encrypted email since OpenKeyChain was introduced into K9.

Environment

K-9 Mail version: Latest as of 2017-02-04.

Android version: LG G4 + Android 6.0 + Kernel 3.10.84

Account type (IMAP, POP3, WebDAV/Exchange): IMAP.

Update 1

I think i know what the issue is.

• Imported public key.
• K9 forced me to generate a temporary signing key.
• I could then send messages.
• As an experiment, I deleted the temporary signing key.
• K9 couldnt send emails.
• I resigned the public key by generating the temporary signing key again.
• K9 still couldnt send email.
• I think deleting and readding the temporary signing key is what caused the issue.
• I suspect (but havnt tried) that deleting all keys, then reimporting, will solve the problem.

Update 2

I deleted all keys in OpenKeyChain.

I then imported my public key again, and verified it with a temporary signing only key.

Its still giving the same error.

Update 3

Uninstalled OpenKeyChain, reinstalled, and am still getting the same error in K9.

When I first installed K9/OpenKeyChain, I was able to send PGP email. If unininstalling/reinstalling OpenKeyChain fails to fix the issue, then I would suspect the issue is with K9.

Start by reviewing the reported K-9 Mail/OpenKeychain reproduction steps and the attached error screenshots, using the listed Android 6.0 and IMAP environment. No source file, test, or entry point is named; the issue is resolved when the reported public-key workflow can send encrypted email reliably.