Mount a Samba/SMB fileshare to your filesystem to reach it through Crossover.
Network shares aren't mapped to the filesystem (like /mnt or /media) any longer and go through a userspace plugin (like FUSE) which is only available to the file manager and native Linux applications. Crossover needs a filesystem mount in order to access the file since it can't go through userspace filesystems.
In a terminal run these commands, changing to match your system.
$ mount.cifs //(SMB IP address)/(Share name) /media/(Mount point name) -o credentials=/root/.servercred,rw
.servercred contains the following:
password=(whatever your password is)
Alternatively, the following added to /etc/fstab works: