Downgrade from 11.10 to 10.xx

Downgrading is not supported, so you'll have to do a fresh installation. If you have another operating system installed alongside Ubuntu, or a storage partition separate from the Ubuntu system, then you should remove your Ubuntu partitions before performing the fresh installation. Otherwise, after you offload any important files, you can just boot the Ubuntu CD and tell it to install using the entire disk.

Upgrading directly from Ubuntu 10.04 LTS or Ubuntu 10.10 to Ubuntu 11.10 is also not supported, though, so I'm wondering how you did that. The upgrade path from either of those versions involves upgrading incrementally to version 11.04 first.

http://askubuntu.com/questions/49869/how-to-roll-back-ubuntu-11-10-to-11-04

As indicated in that article, practically speaking, since downgrading is unsupported and fraught with technical difficulties, and you would't really get a system out of it that was configured the same was as your system was before the upgrade, downgrading is not a good solution to any real-world problem.

If your goal is to have fun attempting to downgrade Ubuntu on a system that you don't currently need to use for any productive purpose, then attempting a downgrade makes sense. At this point, attempting a downgrade doesn't really make sense under any other circumstances.

You are right, but after upgrading my system became slow and frequent crashes, are encountered which i never had..

To be clear, I'm not saying you shouldn't go back from Ubuntu 11.10 to Ubuntu 11.04. And performing a fresh installation of Ubuntu 11.04 certainly *is* supported, including on systems that have formerly run Ubuntu 11.10. It's downgrading a system without reinstalling that is not supported and should probably not be attempted.

Actually its been crashing with the following message in the /var/log/syslog

Oct 28 12:44:53 dwaraka-HP-Compaq-dc7100-SFF-PJ361UA kernel: [16858.172030] [drm:i915_hangcheck_elapsed] *ERROR* Hangcheck timer elapsed... GPU hung
Oct 28 12:44:53 dwaraka-HP-Compaq-dc7100-SFF-PJ361UA kernel: [16858.173866] [drm:i915_do_wait_request] *ERROR* i915_do_wait_request returns -11 (awaiting 1192437 at 1192435, next 1192439)
Oct 28 12:44:53 dwaraka-HP-Compaq-dc7100-SFF-PJ361UA kernel: [16858.173970] [drm:i915_reset] *ERROR* Failed to reset chip

That is why i would like to downgrade, anyone encountered the issue? have some solution, let me know.
Thanks.

This question is about going from Ubuntu 11.10 to Ubuntu 11.04. You'll attract better attention to the specifics of this low-level problem that you are experiencing with the Ubuntu 11.10 kernel by posting a new question about it (https://answers.launchpad.net/ubuntu/+source/linux/+addquestion). I recommend that you do that. If you do, you can post a link to the new question here. Please also feel free to subscribe me to the new question.

Without examining the matter in detail, I can suggest that you try using the old kernel, from Ubuntu 11.04, which if you upgraded to Ubuntu 11.10 should still be installed. You can select the old kernel in the GRUB2 boot menu--hold down Shift while your computer starts up and select the menu item to view older kernel versions. Select the newest version where the first number in the version is a 2 rather than a 3. (Don't select rescue mode.)

You have an issue with management of graphic memory in kernel for Intel GPU. But I can't say more. Pleas link question to "xserver-xorg-video-intel" (or "linux") packet.