Guild Wars 2

You cannot apply upgrade components to this item. For example, i want to apply a poly luminescent upgrade but it only has infusion slots.

The same thing happens with Fervid Cencer back item, you cannot apply poly luminescence because they only have infusion slot.

The Ascended Sclerite Karka Shell? Unfortunatly for the exotic upgrade components, it is intended behaviour
Ascended can only have infusions placed in them.

As for your Fervid Censer, Anomaly listed on the Wiki page “Unlike other non-ascended back items, the Secret of Southsun version has a defensive infusion slot instead of a regular upgrade slot.”
So you have to use other Exotics to place your upgrade components in.