Yup...you are right...it is a custom property.  Here is the code (the corresponding FieldPropertyDescriptor exists):

I even forced the 0 value, if null, to be a decimal (even though I should not have to do that).  What is extremely odd is that the value of the object is {} rather than null (see attached).  Why would the object come back as an empty set rather than null?

This looks like you may need to take something into account within your BO and properties.  For example, the LastInvQty looks as thought it may be a custom property (it may not) but in either case, there is an illegal cast exception.  So the property may be getting evaluated earlier or in a different way than normal.  Put a break point in the Get of the property and see when and how it is being accessed.  Work backwards from there. 

Here is the most recent error message for us to work with...

It worked on the test solution, but my application is not responding the same way.  I am still getting the elusive error.  Any ideas would be appreciated.

Adding the following fixes the problem. 

I will make sure to add these to every BO in which I have created custom properties. 

I duplicated the details I found in the designer file of a BO and this is what I ended up with:

It does not make any difference.  I still get the same error.

The following data retrieval method was not updated properly before I zipped...sorry...

Just delete the " AS ItemCount" from the select statement.  All will be well after that.  I was trying to pull a value for the custom property, but it does not matter.

The details are quite simple (sample app attached). 

1)  Create form.
2)  Add BO (the BO must have a custom property).
3)  Add DevEx GridView.
4)  Add BBS.
5)  Connect BO to BBS and BBS to Grid.
6)  Remove several columns from the grid, including the custom property.
7)  Run the app.

The grid will appear with data filling it (Movies).  Simply close the form and the error will appear.

I know the error is because of the custom property, but I cannot determine why.

From going back and rereading your previous posts, it just sounds like it is a simple matter of creating a custom property and setting using a ReflectionPropertyDescriptor defined in the GetCustomBindablePropertyDescriptors methods.  Just create a custom property that is properly exposed to respect a BBS (look at a property built through the BO Mapper for the required attributes).

We have developers using a DevExpress grid and BBS objects every day.  So I really don't know what you are referring to here and exactly what issue that you are having.  A sample or more details would be helpful.