Reg Error : Two or more nodes are in a loop and will not be started.

A start node can't have any incoming process flow; a start form can't be re-executed under any circumstances.  If you need to loop back to a certain interface, it will need to be added to a User Input Task, which you can loop back to as many times as you'd like.

Thanks for your response.

Can you please tell me if I use user input task,then how can i configure that process model in site?

You can use the same interface in a start form as well as in a user input task.

For what it's worth: i personally almost never use the "configure process model as site page" feature.  It's just not very flexible and not very useful for me.  I strongly prefer allowing a user to click into a process model if they want to, providing a "start process link" setup in a site page interface (which usually has other things on it as well).  Thus I almost never configure a process model with a start form, preferring instead to chain the user directly to the first User Input Task in the process model, which works seamlessly (and assuming you set things up correctly, again provides quite a bit more flexibility).

You can use the same interface in a start form as well as in a user input task.

For what it's worth: i personally almost never use the "configure process model as site page" feature.  It's just not very flexible and not very useful for me.  I strongly prefer allowing a user to click into a process model if they want to, providing a "start process link" setup in a site page interface (which usually has other things on it as well).  Thus I almost never configure a process model with a start form, preferring instead to chain the user directly to the first User Input Task in the process model, which works seamlessly (and assuming you set things up correctly, again provides quite a bit more flexibility).

Many Thanks!!!