Q: unable to buy iPhoto card

Have you set the Print Products Store to a country, where your Apple ID is valid? You set the store in the iPhoto Preferences > Advanced panel:

You do not mention your iPhoto version. Is it iPhoto '09 or '11? Older versions are no longer supported for Print Products,  see:   http://support.apple.com/kb/HT3412

Also, in some countries are print products not yet available:

The Apple Store - International Print Product

could that be because i didn't agree to the location setting of the iphoto?

That is possible. Then some services are not available.

You are quick. I was still editing.

You do not mention your iPhoto version. Is it iPhoto '09 or '11? Older versions are no longer supported for Print Products,  see:  http://support.apple.com/kb/HT3412

Also, in some countries are print products not yet available:

The Apple Store - International Print Product