That may depend on the directory and file rights. If the us who runs smb
have no access rights, you can't read or write files. You can find out file
permissions with ls -la you will also see owner and owner group.
You can try to set read and write permissions for all (chmod 777 directory
-R). If this was the problem, then you should give read and write
permissions only to the user that runs smb. Set permissions for all back to
0 (770) because of security reasons.
Here you find a tutorial on set up samba for Rasapberry