I have integrated my heroku apps in sales force using canvus, every thing was fine , apps were wroking fine in salesforce, but now when i tried to acces my apps in salesforce it's giving the following error 

Authentication Failed: OAuth login invalid or expired access token error

what can be the possible reason of this issue, Guys help. 

I'm working with the Force.com Integration Workbook.  Everything is fine until I get to Tutorial #3! 

The workbook talks about setting up Remote Access; however Remote Access is no longer available and you're redirected back to App | Connected Apps.  At this point the workbook doesn't match the latest version of Salesforce (Summer 13).

Additionally, in Tutorial 3, Step 2, I cannot get the OAuth to work!  I get the error:

HTTP Status 401: Authentication Failed: OAuth login invalid or expired access token

I've set this up twice and I'm following the steps "exactly" as they are laid out in the workbook.  Was wondering if anyone else has come across this and if I'm simply missing something.  I'm pretty new to the coding side of SFDC; so I'm working through these workbooks to try and get a better understanding!

Thank you!