Citrix FAS 12.1 -Unable to launch apps -access denied error on storefront servers

When launching Apps\Desktops user receives "Cannot Start App" or "Cannot start Desktop", and Errors/Warnings on StoreFront "Access Denied", Event ID 1 Error and Event ID 28 Warning...

Unable to start application with SAML authentication "Cannot Start App" Event ID 28 Could not contact any Federated Authentication Servers

Launching an application or desktop fails when StoreFront is configured for FAS/SAML authentication. Error seen when user tries to launch an application or desktop: No errors are logged on the FAS server. Storefront will show event ID 28 with error showing "...Could not contact any Federated...

Cannot Start App - Federation Authentication Service

The application launch fails with an error "Cannot Start App" once FAS is enabled on the StoreFront. On the StoreFront you will see Event ID 28 and on FAS server you will see Event ID 123...