Recently I saw an access denied error when a user tried to edit a SharePoint Designer workflow task. The error did not occur if the user was a site collection administrator, but did occur even if they had full control to the site, list, and task list.
Running through the Request Access pages, it appeared that SharePoint did not think the user had rights to the task list, even though they did after thoroughly checking permissions.
I figured that it was having trouble with permissions to the ASPX pages from the Designer-generated tasks forms, so I solved it by doing the following, by admin account:
– Open the site in SharePoint designer
– Locate the “Workflows” node in the tree view.
– Right-click “Workflows” and select Properties.
– Click the Security tab.
– Choose the option to manage permissions from the browser.
It turns out that this “Workflows” node is actually a SharePoint folder object, and it turned out that this folder did not inherit permissions from the parent. The web page for managing permissions that came up showed me this, and enabled me to reinherit permissions and fix the problem.