Unable to install security patch SUPEE-10266

[sathishm18]

Hi Team, 

When I was trying to run the script (sh ./SUPEE-10266.sh) I am getting below error.

Please check and advise on fixing this issue.

Error : 

-e ERROR: Patch can't be applied/reverted successfully.

checking file app/code/core/Mage/Admin/Model/Session.php
checking file app/code/core/Mage/Adminhtml/Block/Notification/Grid/Renderer/Notice.php
checking file app/code/core/Mage/Adminhtml/Block/Widget/Form/Container.php
checking file app/code/core/Mage/Adminhtml/Controller/Action.php
checking file app/code/core/Mage/Adminhtml/Model/LayoutUpdate/Validator.php
checking file app/code/core/Mage/Adminhtml/controllers/CustomerController.php
checking file app/code/core/Mage/Adminhtml/controllers/Newsletter/QueueController.php
checking file app/code/core/Mage/Adminhtml/controllers/Newsletter/TemplateController.php
checking file app/code/core/Mage/Checkout/controllers/CartController.php
checking file app/code/core/Mage/Core/Model/Email/Template/Abstract.php
checking file app/code/core/Mage/Core/Model/File/Validator/Image.php
Hunk #1 FAILED at 90.
1 out of 1 hunk FAILED
checking file app/code/core/Mage/Core/Model/Session/Abstract/Varien.php
checking file app/code/core/Mage/Core/etc/config.xml
checking file app/code/core/Mage/Rss/Helper/Data.php
checking file app/code/core/Mage/Sales/Model/Resource/Order/Item/Collection.php
checking file app/code/core/Zend/Serializer/Adapter/PhpCode.php
checking file app/design/adminhtml/default/default/template/backup/dialogs.phtml
checking file app/design/adminhtml/default/default/template/catalog/product/edit/options/type/file.phtml
checking file app/design/adminhtml/default/default/template/customer/tab/view.phtml
checking file app/design/adminhtml/default/default/template/login.phtml
Hunk #1 succeeded at 61 (offset 3 lines).
checking file app/design/adminhtml/default/default/template/notification/toolbar.phtml
checking file app/design/adminhtml/default/default/template/oauth/authorize/form/login-simple.phtml
checking file app/design/adminhtml/default/default/template/oauth/authorize/form/login.phtml
checking file app/design/adminhtml/default/default/template/resetforgottenpassword.phtml
checking file app/design/adminhtml/default/default/template/sales/order/view/history.phtml
checking file app/design/adminhtml/default/default/template/sales/order/view/info.phtml
checking file app/design/install/default/default/template/install/create_admin.phtml
checking file app/locale/en_US/Mage_Adminhtml.csv
checking file downloader/template/login.phtml

[Tom Robertshaw]

Are you able to manually check the files where the hunk fails and compare with what the patch is expecting to find. You should be able to find why the patch hasn't been applied. If it's only a small change, then you may be able to manually correct before applying the patch again.