I'd check with Kovid, but it looks like libraries are listed within the file "
gui.json".
Mine shows
Code:
"library_usage_stats": {
"C:/Users/Peter/Documents/Test NewDB": 2,
"C:/Users/Peter/Documents/Sue Test": 3,
"C:/Users/Peter/Documents/Nora": 4,
"C:/Users/Peter/Documents/Peter's Library": 1435
},
which corresponds to the libraries listed in my "Switch To" list. It might be worthwhile shutting calibre down, making a backup copy of that file, and then removing the entry for the non existant libary.