What kind of error message you are getting (Your login attempt was not successful. Please try again)
You could try to recreate the project and set new administrative details.
1. Open your project web.config
2. Find the following line:
|<cms defaultProvider="Sitefinity" pageExtension=".aspx" siteTemplate="" projectName="myproject" disabled="false" pageEditorUIMode="Overlay">
3. Set disabled="true"
4. You will be redirected to the Project Startup http://localhost/your_project_name/sitefinity/cmsstartup.aspx
Hope this helps.
the Telerik team
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