Shadow Shield not upgrading?

I recently obtained a drop from FoW, a gold shadow shield. It's req9 strength and has an inherent damage -2 while in a stance mod (no shield handle upgrade and no inscription slot, obviously). However, when I try to add a +30 shield handle of fortitude, it just won't add on. I double click on the shield handle and scroll over the shadow shield, as usual, but the hammer-type icon that you see when upgrading a weapon has the red circle with a slash though it. Clicking on the shield does not add the upgrade. There's no message that pops up or anything. I'm very confused because this has never happened to me. I've looked on Guildwiki and everything. Please tell me if I'm missing something very simple!

You can not upgrade that shield.
You can only apply mods to shields that have the inscription system, like Nightfall, EotN, or from certain chests.

you can only upgrade Inscribable shields, this includes handles. You can only add or remove handles from inscribable shields.

Yeha you can get drops like that in FoW

Thank you, I don't play core areas often so I was not aware that you could not upgrade the handles on non-inscribable shields.

inscribitions came only after NF, so any items you find after NF have inscribtions on them.

Technically, that is not completely correct. There is a chance for items to drop with no inscription.

It won't help with your shield, but I've been able to add handles to white shields dropped in Tyria and Factions. I've never been able to add a handle to a blue/purple/gold non-inscribable shield though. I don't know if you could add a handle to a gold NF shield that dropped without an inscription slot.

Items in the FoW and UW can drop with or without Inscritions.

Only from the reward chests after completing all quests. Monsters and Phantom Chests/Obsidian Chests cannot drop inscribable items.

Note, for your information this ALSO applies to wand wrappings and focus cores, but not martial weapons (sword/bows/etc hilts/grips).