UPDATE: This issue has been resolved, I had elided a character in editing a custom theme. Read on only if you want to be exposed to my idiocy, and Sven’s helpfulness!
I see a couple other people have reported similar things, which in some cases were diagnosed as falsely flagged errors, but this has stopped my site loading.
Any suggestions welcome. It started after I uploaded of a PNG, but I can’t see how that would be related (there wasn’t a backlash in the file name, for instance).
Well, that wasn’t the most helpful error message. 
What theme are you on and do you have a custom theme enabled?
Hej Sven, I’m using a custom theme, forked from Alpine, on Hugo 0.91 — let me know if I can help any further.
Does it work if you temporarily disable the custom theme and just use the built-in Alpine?
Aha, it does. So some recent change I’ve made has obviously broken things. Can you help me decode the error message to figure out where that might be?
I can take a look if you provide a link to the custom theme’s source code (or paste it here). As I wrote above, the error message by itself is a bit cryptic.
Thanks, here are the three files mentioned in the error message:
If you need to see the whole custom theme, what’s the best way to do that? Do I try and export it from micro.blog and upload it somewhere?
Try changing this in head.html:
<link rel="shortcut icon"https://adam.micro.blog/uploads/2023/3a9f9cbfcb.png" type="image/x-icon" />
into this:
<link rel="shortcut icon" href="https://adam.micro.blog/uploads/2023/3a9f9cbfcb.png" type="image/x-icon" />
Fudge, I skipped a " and wasted a bunch of your time. Sorry dude, and thanks!