It could be a few things, it could be that your clutch release mechanism is not working properly, thus you are getting drag on the gearbox even when the clutch is fully depressed.
Ours cruches as well in 2nd, however only when changing gear at the wrong time, you can drive without a clutch, by changing gear at the right time, and letting engine speed drop to match road speed before pushing it into the next gear or increasing engine speed for dropping gears (did this the other night when my release fork packed in).
So in theory a good gear change does not really need the clutch. You may be aware that some gearchanges just slip in no problem and others are slightly hesitant, thats the syncros working.
2nd usually gets the most use, and as a result fails first, it can be in a state of failing for some time, and the dodgey clutch will not help it, however other gears will cope with good syncros, although feel a bit iffy.
So, you have a worn syncro on second most likly in which case, live with it by changing gear carefully its not worth dropping the box yet (its not hard you can live with it perfectly happily with it).
It could be the hydraulic cylinders is leaking, the fluid is low, or there is air in the system, therefore not pushing the release fork enough to release the clutch.
I would start (and did yesterday) by checking the hydraulic system, if need be bleed it and top up with fluid, look for any leaks around the master and slave.
If your lucky, that will sort it for the sake of 30mins and some fluid.
If all is well with the hyraulics your clutch release mechanism is failing (the piviot point wears through or the fork collapses, or the baring is goosed) your going to need to take the gearbox off the engine to change the release fork anyway and it may be worth getting the gearbox rebuilt, while its off, and check your clutch plate too, for £20 it would be worth putting a new one in to save having to do it again 20,000miles down the road!