I successfully recorded my scenario in Neoload that contains only a few transactions. Then, like described in the Neoload documentation, I launched a user validation but I got some errors. Since the recording went fine, I don't know what can cause these errors.
When you record a scenario, Neoload will store all the requests/responses exchanges between your browser and your server.
You will see in the "Design" the content of this requests and all their parameters.
Some of this parameters will probably be different if you record again the same scenario.
If you try to replay the scenario as is, it may fail.
There are many reasons for a script to have errors on playback (Validation). Here are a list of the most common things to look for and do: