Gnus ignoring ~/.authinfo for gmail

For whatever reason, gnus has been very temperamental with regards to
gmail's imap. In my ~/.gnus.el I have

(add-to-list 'gnus-secondary-select-methods
	     '(nnimap "gmail"
	       (nnimap-address "imap.gmail.com")
	       (nnimap-authinfo-file "~/.authinfo")
	       (nnimap-stream ssl)))

and in ~/.authinfo
machine imap.gmail.com login e-mail <at> gmail.com password psswd port 993

It's chmodded to 600, and yet, every time I start gnus it asks for my
username and password. Sometimes it even asks twice!

More troubling, at random times when I try to access my gmail inbox, I
get the error, Wrong type argument: stringp, nil from the function
nnimap-verify-uidvalidity. When this happens I curse a little, try
renaming .newsrc.eld, which doesn't work, and end up waiting until, for
no apparent reason, it starts working again. It makes me wonder if emacs
really is run by tiny men inside my computer, I'm so baffled.

Does anybody have an idea where I should look to fix this problem?
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