Hi,
Do you have the required plugin installed "Telerik Web Control Support plugin." Also can you provide the following details
1. Screenshot of the Properties & Methods available for the web page in advanced view mode.
2. The technology the webpage is developed is it Silverlight / ASP.Net/ CEF based.
Incase of a Silverlight based application please make sure the xap file is compiled using the testComplete tcAgPatcher.exe .
https://support.smartbear.com/testcomplete/docs/app-testing/web/silverlight/preparing-applications.html