It seems that the shortcode has changed over time, can you confirm this @mbrsolution ?
I had the above error so I tried the WP Cart Shortcode button and it gave me a different shortcode to the one that was previously working.
Old shortcode:
[wp_cart:The Early Years CD (including UK p&p):price:5.99:end]
Current shortcode:
[wp_cart_button name="The Early Years CD (including UK p&p)" price="5.99"]
Perhaps not using the ‘&’ works for the old shortcode, but ‘&’ is working with the new shortcode.