Dear Debarun,
the issue is related to loading the Raman gain profile. the files can be found in the example library located at C:\Users\USER NAME\Documents\OptiSystem 21.0 Samples\Optical amplifiers\Raman amplifiers\.
If the problem persist, email me at ahmad.atieh@optiwave.com and let me know the example that you are experiencing the problem with. Let me know also your institution and the version of OptiSystem that you use.
Regards,
Ahmad