This error message indicates that the read-only setting is enabled on the menu set from which you are attempting to start the workflow.
To resolve this, you will need to turn read-only off by following the steps below.
In the Admin Tool, click User Accounts.
Change the User Filter to All Users.
Locate the affected user, then double-click their user account record.
Click Menu Sets.
Scroll down to the menu set that should not be read-only, single-click it, and on the right, click Change Read Only.
Click OK.