What do I do if I have different Acrobat products for a Mac and PC?

  I have Acrobat 10 for Mac downloaded on my laptop.

I just bought a PC and need Acrobat.  I purchased and downloaded Acrobat XI Standard.  I can't register the new product on the PC.  It says the serial number is valid bu t I must own one of these qualifying products?? 

What do I do?  This is not an upgrade.  This is a new purchase.  I need Acrobat for two different operating systems. 

Thx,

Sherry