Hi i've struggled with this one for a whole day and i thought i could send a flag to others.
50% of the times i loaded a page i got the error, any kind of page not just the "files admin" page that some have had problems with.
reading a lot of posts pointed me on the .htaccess direction.. after trying a few changes and pulling some hair off y did a magic trick!!
from where it was, to the top of the file before
### SILVERSTRIPE START ###
not much of a gandalf trick, but did the job
hope it helps
It turned out to be a matter of DB server load. my hosting provider fixed it for me.