I was having a frustrating problem recently with a brand new site collection in SharePoint 2010. Each time I attempted to create a new FAST Search Centre site an unexpected error would quickly occur with a different correlation ID each time.
This new site collection was in a web application with other site collections where the FAST Search Center sites had been sucessfully created.
After attempting to create the FAST Search Center site several times without success and with very little useful information in the event logs I turned to Google and found the folowing blog post with some useful advice:
The problem was because I had not enabled the ‘SharePoint Server Publishing Infrastructure site collection feature.
Once this feature was enabled I was able to create the FAST Search Center site successfully. It was a quick fix but if I had not found the above blog post it could have taken me much longer to get to the bottom of the issue.