is wrong ban an enumerator child category an enumerator progenitor class?

i've got an blunder build says:

error 12 can't many convert
type
'system.collections.generic.ienumerator< baseclass>'
to
'system.collections.generic.ienumerator< iparentclass>'.
an eloquent reworking exists (are you
blank cast?)

is wrong simply ban away?

this code:

public dictionary<int32, baseclass> map { get; private set; }

public ienumerator<baseclass> getenumerator()
        {
            relapse this.map.values.getenumerator();
        }

public ienumerator<iparentclass> ienumerable<iparentclass>.getenumerator()
        {
            relapse this.getenumerator(); // error!
        }

my doubt is, i only change line:

return this.getenumerator();

to:

return (ienumerator<iparentclass>)this.getenumerator();

(without any bad side effects)?

accepted answer:

i've altered duty following (after reading jon skeet's post):

ienumerator<iparentclass> ienumerable<iparentclass>.getenumerator()
        {
            relapse this.map.values.cast<iparentclass>().getenumerator();
        }