After correlation when try to validate scripts(flash/flex based) through Start checking button it is taking at least 3 minutes to start the process.
When you start a user validation, NeoLoad starts the load generator. Depending on your machine configuration and the size of your project it can take some time.
Is it also taking time when you run a validation of an empty user (add a delay on that user)?
Have you tried to use a remote load generator and see if it also takes same time?
