How to find underlying source of this error? Designer/FormView/ObjectDataSource

In the designer I get this error: "Error Creating Control: Object Reference Not Set to an instance of an object". The page itself runs fine. One of the objects, possibly an objectdatasource has to be failing at design time. But how to find which one?

The project was originally designed with a XSD for the data pointing to SQL Server queries. All based on typical Microsoft demonstrations which don't really take the product lifecycle into account.

I have had to refactor a number of things in the database, and the XSD designer doesn't automatically show you what you need to fix, you just have to run and get a runtime error. Obviously this means that some of the many individual adaptor methods are probably still incorrect, and I'm going through and updating them to match the new database model, and then tracking through the ef开发者_运维知识库fects through all the bound controls and everything. And eventually, I may get away from a lot of this wizard-generated code and have something a bit more able to be statically checked by the compiler during the build.

But for now, how do I find out which object reference is the problem?

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Problem appears to be due to a null Context in code in a base class which worked fine in VS 2008 which was being called in design-time