switch.pm glitch - cannot upload spreadsheet

I was adding hymns to RoA2002, but when I tried to upload the spreadsheet, I got the error message shown in this screenshot plus of course it wiped out the eleven hymns that were already there. I have no idea what switch.pm is, whether it's something that I need to restore (I must have had it in the past because I've been uploading spreadsheets here for years) or something you need to restore (ditto), nor how to do so if I need to. I also don't know whether you can install it for me from the copy apparently uploaded to a temporary folder at your end.