On Home tab are presented Purchase approvals to take action, but I already approved all these purchase orders, 

I see that these orders were altered for another person, after my authorization.

If I try again approve these orders, I can`t do that and its showed the following message:   "P urchase Order is already approved by  you on  25.04.2013 with the below comments "

What I do to solve this problem?

Thanks

Miguel Alessandro