Unexpected error occurred while communicating with Administration Service

Ran into the following issue when attempting to access "FAST Search keywords" from the site collection, even though i could access the fast adminstration from Central Administration. After some investigation i found that the web application app pool account had not be added to the FASTSearchAdministrators group on the Administration node of the FAST Farm (as mentioned in the technet article). After adding the account I was still receiving the error, after wading through the ULS logs i found the wcf service was returning with exception: "The trust relationship between the primary domain and the trusted domain failed". There are plenty of blogs out there detailing the exception, long story short it occurs when Principal.Isinrole is called to check permissions and the group used does not exist. I thought the wcf service was probably looking for the optional Security group and when it could not find it locally was going out to the domain, which obviously has issues. My resolution was to create the optional group FASTSearchKeywordAdministrators group (detailed in the technet article). I then added my app pool account to the group and everything started working as it should.

From the article: "The FASTSearchKeywordAdministrators group is not automatically created during installation, but can be created manually if you want to use this level of authorization."