Re: error on default.aspx
If its not updating ~/Data/currentlog.config then the folder is not writable. If it is writable then you should be able to see the error in currentlog.config
Also your host should see the error in the Application Event Log on the server. Without knowing the error I cannot help, though I am pretty sure the error is that it cannot write to things it needs to write to like the error log, cachedependency files, search index etc.
I know in my hosting environment I use the Plesk control panel but its not dependable to go by folder permissions indicated there.
Hope it helps,
Joe