2 things to look at. Did you re-apply the transports for the new connector and did you create a new connect string, also check the different varibles in the connect string. Qlikview has a habit of changing the default values.
Go to QlikTech's download site, download the transports, them have your basis person re-apply them. Did you apply the new transports for 5.3 ? One other thing to check. Have your security person check to see if the userid you are using is not locked in SAP.