Hello Sanjay Singh,
Thank you for posting to the Micro Focus Community Site. As my colleague Gael Wilson has mentioned, this might indicate that the region was not successfully started.
Also, I want to note that the option for debugging that you are trying (using cassi -a) is no longer supported in recent versions of the product. What version of Visual COBOL Development Hub are you using? You can display the detailed version information - in a Unix/Linux shell that has the COBOL environment is set - with the following command (note the V in the following is Upper Case):
cob -V
And, what operating system and version are you using?
Finally, investigating issues with Enterprise Server can be complex, and might require gathering diagnostics that should not be shared on a public forum. For these reasons (and to get faster assistance) you might want to create a Support Case for this problem.