A Silk Performer 8.1 Browser-Driven Load Testing script executes successfully on TryScript but fails immediately after the BrowserNavigate function when running a loadtest.  

This can be caused by Silk Performer sending an invalid HTTP header during loadtests.  This header can be viewed in the out-hdr tab of the BrowserNavigate function and will be similar to that highlighted in the image below:

The server may respond with an "HTTP 400 Bad Request" (see image below) error rather than the expected response which causes the subsequent functions to fail.

This issue has been resolved with patch SP811_Patch01.