I had exactly this problem too, I asked on the Derelict forums: http://www.dsource.org/forums/viewtopic.php?t=5856&sid=8ebff671fafec3bd8962ddfceaf99eb8
At the moment I've resolved this by building Derelict with make, first a normal full build, then a second run using the cleandi target, which removes the generated di files. I've set up the Derelict lib and include paths in dmd's sc.ini file, so I just have to call 'rdmd main.d' to build and run.
