Hi Raymond,
We had several customers complaining from similar issues before. The main point were either the network/firewall settings, or the browser settings. The best way to identify the reason for the problem is to start with a new PC, not using the firewall and apply the settings of the computer giving the problem to it one by one.
Let me know if I can help with anything else.
Kind regards,
Erjan Gavalji
the Telerik team
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