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.