I finally resolved this issue.

I converted my website to a web application project as per this blog: http://west-wind.com/weblog/posts/533644.aspx

(I thinked that I HAD a web application, but that was not the case).

So after following those instructions, I have no more problems with these #$%%#  errors.

I know others were having similar problems because I've read other posts looking for a solution , so I hope this could be useful.

I have searched all my computer and can't find any more extensibility or addin dll that the mentioned before.

I have uninstalled and reinstalled Strataframe and have the same problem.

When I open a web form and select a webbusinessbindingsource and then click on businessobjectname, the list of business objects appers as they are supposed to do; but, if I open a second web page and do the same steps, I get the error about applicationbasepage not found...

What else could I look for?

Yep, they will be in those locations as well. But they should be the same version as the .DLLs in your GAC.

Well I have Microfour Strataframe Extensibility.dll in

C:\Program Files (x86)\Common Files\Microfour

and in

C:\Program Files (x86)\Microfour\Strataframe

but that is right, isn't it?

This sounds very much like a standard AppDomain / multiple assemblies on the same machine issue.  Be sure that you do not find any other Extensibility and AddIn assemblies on your machine.

I have the same problem , but sometimes it occurs, sometimes it doesn't.

I don't know what is causing it. I followed the instructions given here, but it doesn't solves it. Sometimes I close and reopen VS2008 and it gets solved, but other times it doesn't

I am using Windows Vista Ultimate x64, VS2008 and SQL2005

Extensibility...that is what is attempting to look in the GAC.  I have just tested this over and over again...so there is definitely something not lined up right on your machine.  Here is what I would do:

1. Make sure that you have only a single version of Microfour assemblies in the GAC
2. Go to the c:\program files\common files\microfour\strataframe and make sure that you have the most recent version of the SF assemblies (if you are running the 1.6.6 beta they will be 1.6.5.3 for the file version).
3. You can also verify the versin from within VS by clicking StrataFrame -> Version
4. Next, remove all MicroFour assemblies from the GAC
5. Replace the removed assemblied from the GAC with the ones located in the c:\program files\microfour\common files\microfour\strataframe

It really shoudn't be more complicated than that...that is why this is quite strange.

I also get the same error from within the SF sample web application.

There is only one set of assemblies referenced in the GAC.

If the type editor is looking for the business objects initialized in the ApplicationBasePage in the App-Code folder of my web application, how is it trying to find the reference? Is there something in my app that should also be in the GAC?

Terry

If you have built the project, ensure all of your SF references, made sure that you do not have more than one version of SF assemblies in your GAC, and are inheriting from the ApplicationBasePage on the form producing the error, then I cannot give you a straight answer.  This looks to be an environment issue...but to ensure that you are welcome to post a sample project so that we can verify that this is not an issue with your project or code.  This will at least give a starting point versus a lot of forum posts going back and forth.

This error is thrown by SF when I attempt to select a business object from the property sheet of an SF Textbox on a web page that inherits from "ApplicationBasePage". Since it is looking for the code in my project, if someone could tell me how the "MicroFour StrataFrame Extensibility" is searching maybe I could help track down the problem.

Any help will be appreciated.  Thanks Terry C

Exception
  The ApplicationBasePage could not be located.  Please rebuild project.

Source     : MicroFour StrataFrame Extensibility

Stack Trace:
   at MicroFour.StrataFrame.Extensibility.BusinessObjectNameTypeEditor.EditValue(ITypeDescriptorContext context, IServiceProvider provider, Object value)