You need to provide more context. Was it working before and then you did something and it stopped working? Or are you setting up for the first time? Did you set up all the admin functions? There is some pretty extensive documentation on how to set it up. You can find it here (of course your install would be ST6 or whatever):
Thank you for the kind reply sir. Yes it was working before. but it is giving error while opening. So I would like to know what could be reason or possibility for such error and also solution for that.
Looks to me like a SQL problem.
Search the google for the text in the message box. "Cannot connect........"
I got some hits on it.