yeah, the sdcard is always RW.
well if you have terminal emulator
type
su
mount
and see what /system is mounted as ro or rw
if ro
type(in same terminal session as su)
busybox mount -o remount,rw /system
see if any errors show, or type
mount
and check /system again
**********************
My output using ADB and busybox
# mount
mount
rootfs / rootfs rw,relatime 0 0
tmpfs /dev tmpfs rw,relatime,mode=755 0 0
devpts /dev/pts devpts rw,relatime,mode=600 0 0
proc /proc proc rw,relatime 0 0
sysfs /sys sysfs rw,relatime 0 0
none /acct cgroup rw,relatime,cpuacct 0 0
tmpfs /mnt/asec tmpfs rw,relatime,mode=755,gid=1000 0 0
none /dev/cpuctl cgroup rw,relatime,cpu 0 0
/dev/block/mtdblock4 /system yaffs2 ro,relatime 0 0
/dev/block/mtdblock6 /data yaffs2 rw,nosuid,nodev,relatime 0 0
/dev/block/mtdblock5 /cache yaffs2 rw,nosuid,nodev,relatime 0 0
/dev/block/mtdblock0 /config yaffs2 ro,relatime 0 0
/dev/block/vold/179:1 /mnt/sdcard vfat rw,dirsync,nosuid,nodev,noexec,relatime,uid=1000,gid=1015,fmask=0702,dmask=0702,allow_utime=0020,codepage=cp437,iocharset=iso8859-1,shortname
=mixed,utf8,errors=remount-ro 0 0
/dev/block/vold/179:1 /mnt/secure/asec vfat rw,dirsync,nosuid,nodev,noexec,relatime,uid=1000,gid=1015,fmask=0702,dmask=0702,allow_utime=0020,codepage=cp437,iocharset=iso8859-1,shor
tname=mixed,utf8,errors=remount-ro 0 0
tmpfs /mnt/sdcard/.android_secure tmpfs ro,relatime,size=0k,mode=000 0 0
# busybox mount -o remount,rw /system
busybox mount -o remount,rw /system
# mount
mount
rootfs / rootfs rw,relatime 0 0
tmpfs /dev tmpfs rw,relatime,mode=755 0 0
devpts /dev/pts devpts rw,relatime,mode=600 0 0
proc /proc proc rw,relatime 0 0
sysfs /sys sysfs rw,relatime 0 0
none /acct cgroup rw,relatime,cpuacct 0 0
tmpfs /mnt/asec tmpfs rw,relatime,mode=755,gid=1000 0 0
none /dev/cpuctl cgroup rw,relatime,cpu 0 0
/dev/block/mtdblock4 /system yaffs2 rw,relatime 0 0
/dev/block/mtdblock6 /data yaffs2 rw,nosuid,nodev,relatime 0 0
/dev/block/mtdblock5 /cache yaffs2 rw,nosuid,nodev,relatime 0 0
/dev/block/mtdblock0 /config yaffs2 ro,relatime 0 0
/dev/block/vold/179:1 /mnt/sdcard vfat rw,dirsync,nosuid,nodev,noexec,relatime,uid=1000,gid=1015,fmask=0702,dmask=0702,allow_utime=0020,codepage=cp437,iocharset=iso8859-1,shortname
=mixed,utf8,errors=remount-ro 0 0
/dev/block/vold/179:1 /mnt/secure/asec vfat rw,dirsync,nosuid,nodev,noexec,relatime,uid=1000,gid=1015,fmask=0702,dmask=0702,allow_utime=0020,codepage=cp437,iocharset=iso8859-1,shor
tname=mixed,utf8,errors=remount-ro 0 0
tmpfs /mnt/sdcard/.android_secure tmpfs ro,relatime,size=0k,mode=000 0 0
#
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