'Array Missing' messages during installation attempts relate to .info dependancies , the .

Open : uc_website_xml.info
and change This :

; $Id uc_website_xml.info,v 1.0.0.3 2010/08/06 12:30:00 decastroleon Exp $
name = "Store XML"
description = "Shop RSS Product Feed And Sitemap"
core = 6.x
dependencies[] = uc_product
package = "Ubercart - core (optional)"
version = "6.x-1.7"

To:

; $Id uc_website_xml.info,v 1.0.0.3 2010/08/06 12:30:00 decastroleon Exp $
name = "Store XML"
description = "Shop RSS Product Feed And Sitemap"
core = 5.x
dependencies[] = uc_product
package = "Ubercart - core (optional)"
version = "5.x-1.7"

Notice, that you change core from 6 to 5 , and ubercart version from 6 to 5 .