The action does not exist or you do not have sufficient privileges to view it

It can be for many reasons, the two more common would be

1. User privileges, you have clicked on a task that you do not have access to

2. Implementation: There is a link to a task that does not exist or that another user has accepted.

For discarding the first, someone with admin access should check if they can open it or if it is resigned.

For the second one, the best is first for an admin to go to the monitoring tool and search for that task, so the status can be deducted from it.

Sounds like you might have one of your site pages set to a process model start form where the viewer trying to view the site doesn't have permission to the process model.  If this sounds close, start by checking the process model security and making sure all applicable users have at least "viewer" priveleges.

Hello Mike,

I do think that I have the security set correctly. I am the administrator for this application and object and I still get the error...

I got it to work. Viewer security was not available for some objects. Deleted the site and readded and it is working. Thanks

Cool, thanks for confirming.

I know this is an older post and has been resolved but in case somebody else finds it googling for the issue and it isn't a permission setting I'll give an another solution.  If you are using the action outside of the context of a particular record, be sure you are using the process configured as a Record List Action instead of a Related Action.  It will throw the same error.