[puffyn]

Thanks to Alneyan, I was able to run some tests:

1) It isn't just a display bug. When equipped, the wraith sword shows up as a "fist" in the description and acts like one in battle (or, specificially, it doesn't act as a wraith sword, neither replenishing hit poits nor fatigure).

2) Other-two handed weapons also don't work (I tried a crossbow).

3) I attempted Panther's suggestion, but was only able to equip the wraith sword in two of the three possible slots (by either equipping it before or after another, one-handed weapon). Thus, it is still possible that some "off-hand" cause is at work here, although clearly Kristoffer thinks this is not the explanation.

4) Healing the natarajan restored the ability to use the wraith sword (along with a second two-handed weapon), so my guess is that this is a universal feature of the natarajan, and not related to a corrupt file.