Gparted error when trying to increase /

Help ...

Workstation is running : Red Hat Enterprise Linux WS release 4 (Nahant Update 4)
Kernel 2.6.9-42.ELsmp on an x86_64 with parted version parted-1.6.19-4.EL. I have also tried to boot from a Ubuntu 7.04 cd which has a newer version of parted (1.7 I think) and also tried to run gparted but still the same.

Using /dev/sda
(parted) p
Disk geometry for /dev/sda: 0.000-1907308.000 megabytes
Disk label type: msdos
Minor    Start       End     Type      Filesystem  Flags
1          0.031    196.105  primary   ext3        boot
2        196.106 1500194.882  primary               lvm
3     1500194.883 1516197.128  primary   linux-swap
4     1516197.129 1879997.211  extended
5     1516197.160 1526198.532  logical   ext3
6     1526198.563 1536199.936  logical   ext3

What I want to do is resize /dev/sda6 from 10Gb to 20Gb but keep getting errors, gparted errors and says to do the following : e2fsck -f -y -v /dev/sda6   ...... do this and it reports no problems but still no joy with the resize?

Any ideas?