I have a web page with a WebBusinessBindingSource  and an Infragistics UltraWebGrid. (2007.3)

When I try to set the grid's Datamember property i get the following message:

Nullreference Exception

Object reference not set to an instance of an object

Source: Microfour Strataframe Extensibility

Stack Trace:

at Microfour.Strataframe.Extensibility.WebBusinnessBindingSource.GetView(String viewName)

After that, everytime I click on the grid I get the same message  and have to click on the OK button several times to get rid of it.

More than likely when you upgraded, a bunch of "junk" was added to your web.config file.  Restore just the web.config file to the previous version to see if your error goes away.  They added a lot of tags that can cause issues.  If you use source control then this shouldn't be too hard...just restore the web.config file and keep the previous version and it should make things more smooth.  But whether it will resolve this particular issue I am not sure, it is just the first place I would look.