I have been experiencing this problem recently myself (my issue was
limited to Excel 2000). I would be interested in whether there is a
complete answer to the problem, but things I have found to be factors
that are worth considering are (apply to my current situation but may
be relevant to you):

1. The password problem obviously goes away if the VBA is unlocked
before closing (admittedly not appropriate for the user to know the
password)
2. Files run on a server in Excel 2000 do not always close down
properly which can be seen by going into VBA once the file has been
closed: you should still see a reference to the project remaining.
3. Could be caused by having objects that have not been cleared from
memory properly after use (eg Userforms and Class modules)
4. I have also found that using a TreeView control (version 6 - SP6)
also causes the problem (MSDN did not recognise the problem or offer a
solution that I could see). Removing the treeview from my userform
stops the problem, and re-introducing the treeview brings the problem
back.

I realise this doesn't actually answer your question, but at least it
gives you a bit more information to work on. If anyone can add to this
I would certainly be interest in finding out more (particularly how to
stop the problem).

Kind regards,
Simon Livings.

Ken wrote:

I have built an Excel App that I am trying to get my employer to use.
I have been giving them copys of it for a couple of years and never had this
problem before. I can't think of any changes I have made to cause this.

Now if I lock project for viewing in VBA then when you try to close it demands
the password. You can use the app, save it, but when you try to close it will
not close without password.

Ken