On my Windows 10 64bit machine, I had the problem that IrfanView could not scan any more. Neither with WIA nor with TWAIN. Scan Source selection showed both possible sources, though.
WIA simply did nothing.
TWAIN told me: “TWAIN error”
I could scan perfectly well with GIMP using TWAIN drivers. So I tried everything: reinstall drivers. remove drivers and reinstall them. remove complete Brother Suite (for my MFC-9450CDN). With or without restarts in between. Nothing cured the disease.
I downloaded IfranView’s 64bit version and executed it (just the ZIP, not the installer). This one could scan with the TWAIN source.
When I launched the 32bit version again, this one also worked.
Maybe someone finds this piece of weirdness useful!