Answered question

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:

• Start at the validated response that failed in the Check VU window and use the Compare with Recording button. This will show you what the response was when you recorded your script. This is an invaluable tool, and provides a side-by-side comparison of the validation verse recording of either a request or response. You want to ensure that the request was the same, and what is different about the response.
• Look for dynamic parameters that might need to be handled in your application. Using the process above, you can check if certain values are the same between what was recorded and what was in the playback. If a value was the same, but should be different each time you play your script, then this parameter is "dynamic" and needs to be handled by manual extraction or using the automatic configuration option. Check here for more details on how to do that:
http://www.neotys.com/doc/neoload/3.2/en/howto.chooseExtr...
• Check the Neoload logs for clues to what might be the cause of the failure, possibly turning up the DEBUG level of certain log levels (Help > Open logs folder).
• If you have an issue with a response in which a variable was used for the request, ensure that the values in your variable (like a File or List Variable) are good values. Many times logon credentials are not valid, and can cause issues when replayed.
• Keep a script simple at first. The more complex and long a script is, the harder it is to troubleshoot the issue. Start with something simple and short, and add more transactions later on. Stick to a login, transaction, and logout, type of script at first, if possible.
• Record another script doing the same exact thing as the first. Click certain request of both Virtual User profiles (Control-click), then Right-click on one and in the context menu choose the Compare option to compare the recorded responses or requests. This will give you an idea of what is different between two different recordings, like dynamic parameters.