Can't find project or library

Macro-enabled excel workbook opens, but gives the message "can't find project or library" in a message box.
When I close the workbook excel, of its own accord, opens it again, and again gives the error message.
(It is very frustrating because opening the workbook can take some minutes).

I have sought answers on the web. The standard practice is to open the workbook and look at the References tab under Tools in the macro editor.
The trouble is that in my case the References tab is completely empty!!!
So I am at a loss.
I downloaded the MS Repair Tool, only to find it does not repair .xlsm files. So no joy there.


When I last used the workbook (yesterday) everything was OK. I closed it normally.
Now it seems I have lost my program entirely.


This has happened on several of my workbooks. It is not predictable. I hold my breath and pray that I do not get the dreaded message every day.

There is no code in the workbook that executes when the workbook opens.
The macros are executes using a Button.
The workbook comprises a "SetUp" sheet for user input. This input is quite complex and validation comprises about 50% of the main macro code.
However, the real function is to locate files in a directory and analyse their content from the filename.

I have tried opening the workbook (a) on its own, (b) after first starting excel and loading a new Book1 empty workbook, (c) after first starting excel loading a different macro-enabled workbook which does have the usual top four entries in the VBA References tab enabled. None of these methods worked.
The workbook is on a network drive, so I have tried opening it from a different (but same Windows 10 OS and same Excel 365 update) computer. The workbook always gives me the error message.

One week ago I copied the workbook. This copy opens perfectly, (as did the original workbook yesterday).
I admit that I ran the macro yesterday. It worked. I closed normally and thought no more of it.
The file sizes of the 1-week-old copy and the 'bad' workbook differ by 1 kb (the copy is 6530kB, the 'bad' is 6529 kB)


I am at a complete loss!!

The situation is not desperate because I do have that 1-week-old copy which opens OK.
But the problem is cot confined to this one workbook. I have been suffering it for some months with 3 other macro-enabled books. Sometimes (actually, Usually), they open OK, but I am now in the habit of copying them regularly because Excel can at any unsuspected time, fail to find the project or library.

If you have any ideas I would be most grateful to read them.