My co-author can't post comments. She gets a white screen in the URL of the comments PHP page after going through the reCaptcha authentication process.
What I've done:
She emailed me her password. I got the same error. I cleared the cache and cookies and logged in again. Same problem again.
I disabled reCaptcha. Still having the same issue.
I changed her permissions from Author to Administrator. No change.
The issue cleared when I downgraded her permissions to Subscriber. None of my 20 subscribers report any issues with commenting. I have no problems from my Admin account.