The error message is: "this operation is not supported" or something like that.
EXACT error messages are VERY important. Especially if you want others to find solutions.
You are probably getting: "Operation is not supported by this type of database"
This is because of this function:
procedure TSQLConnection.CreateDB;
begin
DatabaseError(SNotSupported); // SNotSupported = 'Operation is not supported by this type of database';
end;
That is the NOT-overruled procedure for CreateDB in TSQLConnection.
But when choosing "PostgreSQL" it should create an instance of TPQConnection automatically (I thought it worked that way).
Apparently it doesn't do it correctly.
Maybe this is due to your TSpecialConnection.
Could you (besides the TPQConnection) try the TSQLConnection directly (without the TSpecialConnection).
Did you add pqconnection in your uses clause? (maybe it only works when you do that)
Otherwise the postgres unit (with TPQConnection) might not be registered and TSQLConnection can't make a TPQConnection from it.