The recent release of Salesforce activated a critical update that revoked basic access to Custom Settings for users who do not have the "Customize Application" permission. Please review the article linked below for more information and instructions on enabling access to custom settings via Profiles and/or Permission Sets:
Salesforce Content must be enabled in your org prior to installing StickIt 3.7+. Follow steps 1 & 2 outlined in the "Set Up Salesforce CRM Content" documentation.