There are many possible reasons that could cause this issue. In order to investigate it we will need more detailed information:
1. Send us the execution log.
2. Please record a Jing video demonstrating the entire process, so we can better understand what is happening.
3. Please provide us with a copy of your test and if it is possible grant us access to your application so we can reproduce the issue on our end and give you a solution.
You can increase the ClientReadyTimeout that specifies the amount of time to wait for the browser to return to a ready state (finish loading the web page). You can do that from the Test List Settings(if you are running your test as part of a Test List) or from Quick Execution Options(if it's a Quick Execution).
Another possible solution you can check is explained in this article.
Looking forward to hearing from you.