Hi,
Configuring authentication :
On the array name, in the Forefront TMG Management console, on the Tasks tab, click Configure array properties.
Click the Configuration Storage tab, and then click Select.
Click Authentication over SSL encrypted channel.
A digital certificate must be installed on the configuration storage server to enable authentication to the Forefront TMG computers in the array.
Assigning roles to users :
On the array name, in the Forefront TMG Management console, on the Tasks tab, click Configure array properties.
Click the Assign Roles tab.
Are you using user in the Enterprise-level administrative roles ?
Thanks