podría haberlo hecho

During my Spanish lesson, my spanish teacher explained to me that
instead of the spanish sentence:

Habría podido hacerlo
Ik zou het hebben kunnen(*) doen
I would have been able to do it

he would normally say:

Podría haberlo hecho
Ik zou het kunnen hebben gedaan
I would be able to have done it (?)

but even though we recognized the grammatical difference, we were not
able to distill the difference in meaning.

Is there any? If so, what is it?
Are the english translations accurate enough?
Is there a difference in usage of both spanish sentences?

René



(*) compulsory Infinitivus Pro Participio (Ersatzinfinitiv) in Dutch.

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