Been awhile since doing anything with jmeter and the first time against a ASP.NET application. Don’t ask me how I managed to avoid it for so long! Anyway I needed to pull out the viewstate to correlate the script. Due to the power of the Internet I found this on how to set up the Regular Expression Extractor.
However, it didn’t work for me. I ended up using this
__VIEWSTATE" value="(.+?)" /> without any problem although it may not be an efficient.