This could be one of two things. First, check your database connection to make sure that it can connect to the StrataFrame database. To do this:
1.) Through Visual Studio, click on StrataFrame -> Database Connection...
2.) This will bring up a database connections window. You should already have an existing connection, if not this is definitly your problem. If one exists, select it and click "Edit", if not, click "Add.."
3.) This will allow you to modify the connection to your SQL server. This should be the same server that you provided when deploying the StrataFrame database during the installation process. Click "Next >" and then "Finish" once the connection has been checked.
4.) Now try to go back into the Business Object Mapper
If this doesn't help, try to open Business Object Mapper through the sample VB application. The Business Object Mapper should appear, if so, then we know that there is something within your current solution that is causing the problem. Let me know if this works.
I know that you are working on a web application. Where are your business objects located? Are they in the website or do you have them in a class library DLL? Just FYI, you will have problems housing business object within a website project itself. This is due to the nature of ASP.NET and how objects are reflected. By housing the business objects in a separate DLL you will just need to add a reference to the web project and add an "assembly" reference on the web.config file. This is the recommended approach for any ASP.NET application. If you are creating custom controls, it would be a good idea to keep them in a separate solution as well.