Need to restrict the user not to delete when the status is in checkout

Hi,

https://dynamicsuser.net/cfs-file/__key/communityserver-discussions-components-files/11/pastedimage1505461798234v1.png

When the status is in open v can allow the user to delete the line, but once it has been changed to checkout need to make the user cant delete the line..

I overrided validatedelete method in line:

public boolean validateDelete()
{
AX_SubscriberMaster axsm;
AX_BookMaster axbm;
AX_TransactionHeader axt;
AX_TransactionLine axtl;
boolean ret;
;
ret = super();
if(axt.Transaction_Status!=Transaction_Status::Open)

ret = checkFailed("Can't delete the subscription");
return ret;
}

But it's making me to not to delete the transaction header, but wat i want is not to delete the transaction line  wen it is status changed to checkout..

How can i do tat?

Thanks in advance.