Access Denied Exception while invoking portlet from MWS

I am getting an Access Denied exception while invoking a portlet from MWS.
The Portlet will invoke a flow service in the developer which in turn updates some data to the database(Internal ACL has been set to which Administrator is a part and we are trying to access the portlet through Administrator).

Attached in this incident is a snapshot of the error message we are getting.

When we try to develop a simple portlet which will add two numbers, It does not give any error message but when we try to develop a more complicated portlet which invokes a service which will in turn invoke child services, we are getting this message.

Can someone please help us with the root cause of this issue.

Also kindly let me know if you require logs from our servers.