There's only 2 possible reasons for this;
1: The drives are exported as Read Only.
2 : The service is set to Read Only.
I would check from the services menu and make sure FTP is set to RW
Quote:
SERVICE CONFIGURATION MENU
Currently Active ( TELNET HTTP RSYNC FTP SMB/CIFS NFS AFP DAAP/MDNS UPNP )
1 - TELNET [ ON ] (ON, --)
2 - HTTP [ ON ] (ON, --)
3 - RSYNC [ RO ] (RW, RO, --)
4 - FTP [ RW ] (RW, RO, --)
5 - SMB/CIFS [ RW ] (RW, RO, --)
6 - NFS [ RW ] (RW, RO, --)
7 - AFP [ RW ] (RW, RO, --)
8 - DAAP [ -- ] (ON, --)
9 - UPNP [ -- ] (ON, --)
M - DAAP/UPNP OPTIONS
S - Status Update [ 01 ] (01, 05, 10, 15, 30, 45, 1h, 4h, 8h, --)
R - Return To Main Option Menu