I'm wondering if they might have somehow become twisted around each other inside the mast -- one idea I'm going to try is feeding them into the mast (not too much) at the mast exit to give them a little play internally and hopefully untwist them, if that is the case. A local marina (Brewers Glen Cove) thinks they'll be able to look at it this week, but I'm a little impatient and was hoping to race next weekend.
I have no choice but to address it now -- the stick *may* need to come down unless I don't decide I don't need a mainsail. What a friggin' mess...
Don't know if it will help you or not but here goes.
If the halyards are internal then there is no way that they could have "become twisted around each other inside the mast". Unless of course one came partially out and was re fed.
It is possible that they got twisted when they were first ran but that's the only way.
You can usually tell if the halyards are wrapped around each other by pulling one and watching to see if the other moves a little. Unfortunately, it sounds like neither one of yours are moving at all.
If you had wire/rope halyards, the first thing I would look for is whether they jumped the sheave. Unlikely both would have done so at the same time though.
My best guess in your situation is that the throat of the splice has jammed into the sheave or masthead. Not an uncommon occurrence. Only way to tell is to go up and look.
If you find that you have to remove a halyard and need to run it through again, you might actually have better luck doing it with the mast up.
My preferred method is to take my weighted messenger and depending on which sheave I am using, I'll have a few guys stand on the rail to heel the boat over so that the messenger slides down the side of the mast keeping it from tangling up with anything else.