Working with AJAX and ReportViewer controls with VS2008 in an Web Application, we've got suddenly a problem: the designer file for a WebForm won't update.
The error in VS error pane sounds:
Generation of designer file failed: The method or operation is not implemented.
After a numerous tries and web searches the workaround is:
1. Delete designer file.
2. Restart VS and reopen the project (important step!).
3. Open a context menu on a victim page (.aspx) and select "Convert to Web Application"
The designer file with correct entries appears immediately.