Nero Express- The disc you have inserted is not empty

Hello Guys Here. I am using nero for burning files. But when I am trying multi-session burning, this error appears. What can I do for me to not encounter this one? Is it safe if I click yes for this message? Please help me guys. Thanks.

Nero Express
The disc you have inserted is not empty, but the writing mode of your compilation is ‘Start multisession’ or ‘No multisession’. This will cause the information already on the disc to be inaccessible via Windows Explorer. Should Nero proceed with writing to the disc?
