How to Call OAF Page from Workflow Email Notification

In R12  below error will occur if you try to open an OAF Page URL link directly.

You are trying to access a page that is no longer active. The referring page may have come from a previous session. Please select Home to Proceed.

Note: When you call a standard page this error won't appear. This happens only when you try to open a custom page.

Below are the steps to resolve the error:
1.Open the custom page in Jdev and select the PageLayoutRN. In the property inspector set the Security Mode to selfSecured.
2.Set the rendered property to ${oa.FunctionSecurity.}
Eg: ${oa.FunctionSecurity.XXCUSTPG}
Note: Your user id should have access to the custom page function.
3.In your workflow procedure generate the  OA page URL with the below function and set the workflow attribute with the generated URL.

lc_url:= FND_RUN_FUNCTION.get_run_function_url(p_function_id => 53637,
p_resp_appl_id => null,
p_resp_id => null,
p_security_group_id => 0,
p_parameters =>'PARAM1='||p_lease_id,--'&'||'LeaseId=784',
p_override_agent => null,
p_org_id => null,
p_lang_code => null,
p_encryptParameters => false);

Now you should be able to open the OAF page from workflow email notification.

Source:http://www.oraclearea51.com/contribute/post-a-blog-article/how-to-call-oaf-page-from-workflow-email-notification.html