Error: type XXX is not an expression

[Era Scarecrow]

   I feel like i need to fully re-learn and familiarize myself with
D now.

   This is an interesting error I'm coming across, it's not
pointing to anything in particular. I've used the -v verbose flag
and it seems to appear each time after a struct declaration.

code      subrecord
function  smartmerged.subrecord.Changes.__xopEquals
Error: type FlagStates is not an expression
Error: type FlagStates is not an expression

The struct is as follows:

    struct Changes {
      string fileFrom;  ///
      Flags state;      ///previous state, be it master/plugin, or
whatever
      ROMBuffer oldData;///the data in question
    }

aliases referenced from Changes:
    alias immutable(ubyte)[] ROMBuffer;
    alias HandleFlags!(FlagStates, int) Flags;

    enum FlagStates {
      def = 0x0,
      changed   = 1,
      readOnly  = 1 << 1,
      isOriginal= 1 << 2,
      invisible = 1 << 3,
      //other states, truncated for example
    }


    struct HandleFlags(E, I)
      if (is(E == enum) && isIntegral!(I) && isFloatingPoint!(I) ==
false) {
        // Yeah a lot of stuff in here.. binary flag handling
        // in my GitHub somewhere.
    }

   From what I can see, the default opEquals is breaking as it's
doing something. This used to compile and has needed some tweaks.
I'll see if I can compile enough to duplicate this simply.