Multiple characters suddenly can't use their items

Hi everybody,

I have a Paladin who suddenly can't wear her scale mail, helmet, bow or two-handed sword, as well as a Fighter/Druid who can't use his scale mail and helmet. They're both still equipped, but they're marked red, and if I take them off, I cannot equip them again.

I have no clue what's going on. Both have no status effects affecting them. No other characters seem to be affected. I am currently in the Vale of Shadows, where I've done all crypts except Kresselack's, and I was on my way to return to Kuldahar with a boatful of loot.

My Paladin is kitted with a kit from A Frozen Journey, but my Fighter/Druid is not.