Cannot create duplicate task from an existing most recent full backup in backup exec 2014

Hello

I am using backup exec 2014. My backup server is windows server 2012.    I am backing up my exchange server usig backup exec.  I have been successfully full and incremental backing up the server.  However, I needed to move my backup to off-site location.  So, I decided to create a duplicate backup from an existing full backup , by which I can assign that backup to a particular tape and then move it to off-site. But the problem I have faced is that out of 3 duplicate backup jobs I have created on this exchange server, two were failed  with an error "Schedule specified for incremental task is invalid".

The steps i created that duplicate task and by which the error was produced is the following:

1. Edit the job.
2. Add stage "duplicate to tape".
3. Selecting media set.
4. Create without schedule "because I want to run this once and manually"
5. left everything else as default and then pressed OK.

 I have attached the error message in the attached file.