[ExternalException (0x80004005): A generic error occurred in GDI+.]
IpitchitImageHandler.Data.ImageRepository.AddNewTempImage(Stream image, String extension, Guid
Everyone here (and on this site) has discussed this as due to a permissions error. I've stumbled over another flavor: memory. I ran out of memory and started receiving this error as well. So keep that in mind as another potential source of error.
In my particular case I was running in a .NET application, and running against a number of threads (few enough that I wasn't being held back too much by the GDI+ process-wide lock). Adding a "GC.Collect()" after major tasks finished didn't seem to affect the speed much, but did completely get rid of the out of memory errors.