Getting Error while create the database copy.

Harpreet_Singh  Whats the current status of that database copy on that server? 

Get-MailboxDatabaseCopyStatus

Generally you can just update it to fix 

If its not suspended or throws an error that it needs to be suspended use  Suspend-MailboxDatabaseCopy

then:

Update-MailboxDatabaseCopy  <DB01\Server> -DeleteExistingFiles