Backup Exec 2012 exchange backups

Dear All,

First of all thanks for the help, Im having some issues backing up the exchange DB i have the folowing screen:

As you can see i got the mailboxes but with no size, Now if i want to select the DB file from the source i got a GREY CHECK so i cant backup the file:

Maybe someone can give me some tip about backing up this files

the exchange version is 2007

the master server and the client are on a windows server 2008 std Edition

Thanks again

Alejandro