Well,
Its just like OP says - the solonoid is faulty.. Youll need to buy a new/2nd hand one and youll have to take the door card off come hell or high water.. Its a common problem
My freeleander did it on the drivers front door to start with, then the passenger front door went.. they all locked no problem, but when i pessed the unlock button, only my rear doors and boot opened..i bought a solonoid for each door off ebay for about £33 each, then took about 45 mins per side to fit them (and grated the skin off my knuckles!)
There are no other suggestions really... as for your door card, mine popped off easy enough.. you sure that youve undone all he screws and popped all the rivets??
At the end of the day, it depends on how much you want the door to unlock.. if you can put up with reaching over from inside to unlock it, leave it and spare your door card (if it really is that stuck).. if its something you really want sorted, then you'll have to get the door card off, even if it means breaking it..