关于delphi xe5 重载的疑惑

[zhu_jiang]

1.我有一父类，方法声明如下，实现忽略
protected
function BeginTransaction:ITransaction;overload;
function BeginTransaction(contextID:String):ITransaction;overload;
function BeginTranscation(contextID:String;isolationLevel:TIsolationLevel):ITransaction;overload;
function BeginTransaction(isolationLevel:TIsolationLevel):ITransaction;overload;
procedure Commit;
procedure Rollback;
procedure Synchronize(trans:ITransaction);

子类集成与该父类，声明如下
TObjectBLL = class(TBusiness)

问题，在子类方法中调用BeginTransaction（没有输入参数的那个方法）,只有BeginTranscation(contextID:String;isolationLevel:TIsolationLevel)能够调用，其它重载方法调用时全部编译不通过，提示[dcc32 Error] Business.pas(100): E2250 There is no overloaded version of 'BeginTranscation' that can be called with these arguments
我到底问题出在那里？请各位大神帮忙解答!!
调用方法如下
function TObjectBLL.Insert(entity: TJSONValue; AutoPK:Boolean): Boolean;
var
dal:TObjectDAL;
tran:ITransaction;
begin
dal := TObjectDAL.Create;
try

tran:= BeginTranscation();
finally
dal.Free;
dal:=nil;
end;
end;

[sololie]

function BeginTransaction:ITransaction;overload; function BeginTransaction(contextID:String):ITransaction;overload; function BeginTranscation(contextID:String;isolationLevel:TIsolationLevel):ITransaction;overload; function BeginTransaction(isolationLevel:TIsolationLevel):ITransaction;overload;

[zhu_jiang]

的确是自己大意了