Melvin,

Did you check if there are any session keys in the response that have to be correlated? If not, please check the initial responses of the script for a key which changes for every different session.

Steps to do that:
1.) Create a sample script to log in.
2.)Run Check Vuser to see the differences in validation response and recorded response.
3.)Check for unique identifiers which would be usually alpha numeric values and then correlate it by capturing it into a variable and use that variable wherever a request uses the session key,