What does Excel mean by 'ExcelVB'?

Background: I had split up an existing .xlam add-in, and I did that similar to the way described at https://trumpexcel.com/excel-add-in/. But now, whenever I open Excel, it gives me two consecutive “Exclamation” messages:
Excel cannot access 'ExcelVB'. The document may be read-only or encrypted.
101070
'ExcelVB' cannot be accessed. The file may be corrupted, located on a server that is not responding, or read-only.
100101
Also, when I open a spreadsheet that contains a function defined in that module and recalculate the cell that contains it, it displays "#NAME?", while the function name is prepended with "'<absolute path to xlam>'!", where the absolute path is C:\Users\<my_name>\AppData\Roaming\Microsoft\AddIns. I had added a reference to that path to the spreadsheet (in VBA editor) and saved the file explicitly (from the VBA editor), but it is not displayed anymore on reopening.