I can't install Acrobat Pro XI on my new computer, get error code 1500, which says another installation is takn place. Not so. Any ideas?

I can't install Acrobat Pro XI on my new computer - keep getting Error Code1500 ("another installation taking

place"). Not so. Any ideas? I know Adoe is trying to force  me to buy a new product, but I'm  satisfied with Pro XI.