How to debug Performance Scripts Issue in Loadrunner

Here are my thoughts:

1. Do you have content check points in your current load testing scripts?
If not, adding check points on the most critical actions for tracking; This is very important for the performance scripts design:
You may want to Check these:
http://joychester.blogspot.com/2009/01/lr-scripts-debuging-on-controller-try.html
http://joychester.blogspot.com/2009/03/content-check-for-web-service-calls-2.html
http://joychester.blogspot.com/2009/02/content-check-for-webservicecalls.html

2. Try to isolate the problem，not mix everything up at the same time.
You can run just one performance scripts at a time which has the problem, and you can run it under different user load, so that you may reproduce the issue easily or just guarantee that this script has no problem;

3. Checking the very first error you met in your scripts.
Usually it is the first thing you need to be caution when you running the load testing. Because it may trigger a tons of following errors, if you did not do error handling well

4. Try to look at the parameters/correlation value you use within the scripts.
This is a check point when you find there is an error on your scripts, make sure you use the write parameters/correlation value before you start to do other deeper investigation. It is not easy to find if you do not know the application very well

5. Of course you should run your scripts in Vugen successfully before running it in Controller.
But I want to remind is that you have to validate all the parameters or situations you may meet, such as using different accounts, different data, also do the Branch coverage if you have "if-clause" in your scripts. So you may get my idea--"Do your unit test on your test scripts" :)

6. Sometimes or more often,The errors may just related to the load you add to the system, not caused by scripts itself.
This errors are only reproduce under a certain load, so it might not be a scripts issue... You can do a load test on your scripts to verify your idea--10 users load, 20 users load, 30... till you get such an error.
But one kind of error is not related to the load, for example, you just input one column which need to be unique value, but in your scripts does not implement this well, so that in Vugen(single user load) or even low load you will not get kind of error, however, if two thread generate this value at the same time, then you may get duplicated value for these two users...thus, you will get an system error,but actually this is absolutely a scripts issue! Be careful!

7. Last and the best practice--After running your scripts in Vugen, please look at your application whether the scripts make the action happen or not, you should believe your eyes, right? :)