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For the Login control we are using a the regular ASP.NET Login control wrapped up in an .ascx file. However sometimes there are some problems with setting theses properties from the UI. However you can set this property in the markup of the user control. To do this go to ~/Sitefinity/UserControls/Login/LoginControl.ascx
and add the DestinationPageUrl property to the login control tags:
This should do the trick.
All the best,
the Telerik team