Cannot read spreadsheet open in Excel; error message is uninformative

[4er4er4er]

If a spreadsheet is open in Excel when "read table" is invoked, amplxl cryptically reports:

Error reading table dietFoods with table handler amplxl:
Cannot extract workbook.

Nicolau observes: As far as I know this is an Excel issue. Unless you open the file in read only mode Excel will lock it and prevent access from other applications. In Libreoffice we are able to read or even write with the file opened (must reload the file after).

Ideally the table handler could tell that it's trying read from a file that's open in Excel; then it could report something specific like "Cannot read workbook while it is open for writing in Excel." Otherwise the new spreadsheet handler could work like the current one, by adding "Is the file open in another application?" to the message. But if we take that approach, we should consider whether there are any other common "Cannot extract workbook" cases that our message should mention.