I had this same problem today. I'm looking for the solution.
Apparently, the error is a PHP error caused by having too many files or folder within a folder. The problem is that I do not have more than 100 in any particular folder, which falls way short of a recommended limit of 32,000. So the problem must be that I'm on a shared server and the combined number of folders within some folder is too many. Dreamhost, you're better than this.