Suddenly can't equip my weapon

When I logged on today I noticed that my weapon wasn't equipped and it also wasn't in my inventory so I freaked out a bit but later noticed that I had gotten mail. When I checked my mail I had a message from the server saying that there was an issue with equipping my weapon and my weapon had been sent to myself via mail. I tried equipping it again and it just keeps saying that the item cannot be equipped.

The item in question is: Smoldering Claw (polearm) and my class is a Warrior. I have used this weapon since like level 50 (I am now 61) without any issues.

In case you have Fury spec, be sure to not have any other weapon equipped (because http://wotlk.cavernoftime.com/spell=46917 does not affect polearms)

So, you can equip that 2-hand polearm only if no other weapon is equipped

You must've changed spec to fury after hitting 60.
After switching talents, you took one-handed weapon in off-hand slot. Thing is, after obtaining Titan's Grip it restricts you even from equiping polearms, so logging out reseted you and caused such thing.