This error is too generic to provide any relevant feedback about your issue. Do you get that error when running a check user path or only when running a test?

Do you get more details about the error?

If you got an HTTP 500 error from the server and then the Silverlight errors it may indicate that those Silverlight errors are only consequences of a previous issue that caused that HTTP 500.

Again it's difficult to troubleshoot your issue in that forum without seeing the project and the user check validation.

I would suggest you to run your test in debug mode hitting the "debug" button to start your test instead of the regular start button. Try with a minimum user load to reproduce and then when the test is over go to your Test results in the Details tab where you should see your user iterations in error. From here you should be able to see the whole user journey in order to check if everything went fine prior to the HTTP 500 error and/or what has been sent on the request that raised that HTTP 500 error.

I guess it's the best way for you to troubleshoot your issue.