Why do you think the problem is a class not found? From that error message, I see two possibilities:
1) employeeTwo does not exist (but that's not the case, you just declared it).
2) class CompanyEmployee does not have a method setAllowance that takes an int, long, float or double (and this must be the case).
Which class defined method setAllowance? If that's Manager, then you need to declare employeeTwo as Manager to be able to call that method.