[SalesForce] Insufficient Privileges error while clicking on any tab in salesforce

You can query the UserRecordAccess object to find out if a particular user has edit access to a record. Something like this should tell you if the particular user has edit access to the particular record.

select RecordId, HasEditAccess from UserRecordAccess where UserId = :UserInfo.getUserId()
and RecordId = :id]

I wrote a blog article about this a while ago that has some more details.

Seems like there is no work around to Use 'login as' feature with SAML enabled and if there is any, they are considered to Security Holes in the implementation by Salesforce.

I got this excerpt from one of the Salesforce Knowledge base mentioned here http://help.salesforce.com/apex/HTViewSolution?id=000175641&language=en_US

Insufficient Privileges when logged in as another user

Knowledge Article Number: 000175641

Description

User has implemented a SAML SSO solution from Salesforce to an external Java app using Salesforce as the identity provider. We're using the FederationIdentifier field from the standard User object in the SAML assertion. The solution works great when a user is logged in as him/herself, but it doesn't work when a user is logged in as another user and giving Insufficient Privileges error.

Insufficient Privileges

You do not have the level of access necessary to perform the operation you requested. Please contact the owner of the record or your administrator if access is necessary.

Internal Diagnostics:

Cannot use IdP while SU'd as another user system.security.NoAccessException: Cannot use IdP while SU'd as another user

Resolution

The error message explains it nicely : We actively block SSO logins when you are logged in as a different user. 'Login as' is meant to enable Salesforce admins to support their salesforce users but it can definitely not be used as a 'backdoor' to gain access to other systems as that user. That would be a huge security hole no.