Wiki Page: Why do I get the error "DOTNET: 3 - Loading object throw exception! Possible reasons: Wrong version of perfdotnetfw.dll, unhandled exception in constructor or insufficient permissions"

If you can successfully run a Try script and you encounter the error when running a loadtest with more than 10 Virtual Users then its possible your application is not thread safe. So you will have to ensure that each virtual user creates their own PerfRun process. To resolve this issue, deselect the "Automatic calculation" under Settings | System | Workbench | Control | and ensuring that the "virtual users per process" is set to "1".   Old KB# 17132