LoadTestAgentResultsLateException - Results from agent Test Agent were not received in time to be included in the overall results for a sampling interval

Exception

Results from agent 'Test Agent' were not received in time to be included in the overall results for a sampling interval. To avoid this error, increase the sample rate, or decrease the load on this agent

Explanation

Sample Rate property for the load test run setting based on the length of your load test.

Solution

To specify performance counter sampling rate in a run setting

1.Open a load test.The Load Test Editor appears. The load test tree is displayed.
2.In the load test tree, in the Run Settings folder, choose the run setting that you want to specify the sample rate for.
3.On the View menu, select Properties Window.The load run setting's categories and properties are displayed in the Properties window.
4.In the Sample Rate property, enter a time value that indicates the frequency at which the load test will collect performance counter data.
5.After you have finished changing the property, choose Save on the File menu. You can then run your load test using the new Sample Rate value.

Load Test Duration - Recommended Sample Rate
< 1 Hour - 5 seconds
1 - 8 Hours - 15 seconds
8 - 24 Hours - 30 seconds
> 24 Hours - 60 seconds

Reference - http://msdn.microsoft.com/en-us/library/ff423846.aspx