When I tried to create a new Enterprise Wiki site I got a general error message with a correlation ID. Checking the ULS i found the following error:
"Detected use of SPRequest for previously closed SPWeb object. Please close SPWeb objects when you are done with all objects obtained from them, but not before"
Not much help. But I found another artical by Todd Carter, who had debugged the issue, that activating the SharePoint Publishing Infrastruture would fix the issue. I had this feature already activated, but deactivating it and activating it fixed the issue in my case as well.