Hello There,

first of all, I suggest you to use the new Lightstreamer JavaScript client version 6 instead of using version 5. The new client heavily simplifies the engine and connection handling so that it is much easier to code with it.
Version 6 is currently in beta version but the final release will be deployed in a matter of days.

NOTE: all of the below comments only apply to the old client version (html client 5)


when he types in a new user / pass and clickes again on submit, there comes an Exception 'ER createEngine() has already been called createEngine '.
If in the code that is called upon submission there is a createEngine call then the message is correct: you should call it only once.

but engineRef is null at this point of time.
during the onEngineReady execution you should save the engineRef pointer somewhere (e.g.: a global variable) so that you can access it later again. In this case do not forget to implement the onEngineLost event to delete the saved reference.

when i check up the login and it is correct, how can i redirect to the next page?
This heavily depend on your interaction design.
Note that if you redirect the user to a different html page you would lose the connection (i.e. you would need to authenticate again).
Check the client guide for an overview of website-integration possibilities: http://www.lightstreamer.com/distros...ient%20Dev.pdf