I have a very challenging issue for you. I have created a custom addin that
contains common code that can be used across many workbooks. I add a
reference to the addin in my workbook and the 1st time that it calls the
addin, things run fine. If I then save the workbook, reopen and call the
addin again, Excel crashes. My issue can be duplicated by doing the
following.

1) Close any other workbooks in Excel, so that you don't lose anything.
2) Create an addin with a single function ... say ...
Public Function ReturnString() as String
ReturnString = "Test"
End Function
3) Save this addin locally
4) Create a new workbook
5) In the Visual Basic Editor, add a reference to this addin
6) Create a button on Sheet1 and have it point to code that says ...
Range("A1").value = MyAddin.ReturnString
7) Save the workbook, click the button and everything works fine.
8) Now, delete the text from cell A1, save the workbook and close Excel.
9) Reopen the workbook and click the button.
10) Observe Excel crash

Why is this happening?

Would anyone be willing to take this on? It will take about 5-10 minutes to
duplicate. It is killing my coworkers and me ... we can't figure it out.

Thanks in advance,

Scott