Opportunity based on Account Role code

Dear All,

We have a requirement to allow users to create Opportunity only for certain role codes ( Eg: Prospect and Customer) of selected account.

I have written following ABSL in Validation-OnSave:

***************

import ABSL;

if (this.ProspectParty.RoleCode == "0001")
       {
     return true;
    }
else
{
raise Inv_cust.Create("E");
return false;
}

***************

Whatever the Account selected it always return  this.ProspectParty.RoleCode as 31.

Any idea on how to get Correct Role code of selected Account during Opportunity creation process.

Thanks and regards,

Raju