Well, I assume that you did also release the forestay from the bow? (that wasn't mentioned, however..please don't be insulted by that question.... it isn't meant that way. We have all made those type of first-time, seems like I forgot something, mistakes!) Other than that..... I can't see anything stock that would prevent the mast from pivoting down towards the stern once the forward pin was removed from the mast hinge.
Thinking back over those "first-timer" mistakes I've made, I recalled a few things that might help..... After you released the forestay, is it possible that the forestay/furler caught on something like a cleat or the bow rail? Did you release the furling line and pull it out of the fairleads along the deck leading it aft? That would stop the mast from lowering.
As another option, you could release the backstay from the stern, remove the aft pin from the mast hinge and pivot the mast down towards the bow. If you have a roller-furling jib, you will also need to release the forestay from the bow to lower the mast forward and be very careful not to bend the aluminum luff extrusion ofthe furler as you lower the mast (If you have a CDI Flexible-Furler, with a plastic luff extrusion or a Schaefer Snap-Furl, this is less of a problem as they will flex quite a bit without kinking, but it is still best to release the forestay and guide the furler down as you lower the mast forward.) I am resonably sure the 240 was designed to allow lowering the mast aft towards the stern normally.
It is possible that the mast has been stepped (in place, vertical) for so long that the aluminum spacers inside the mast hinge may have corroded enough to fuse the two parts of the hinge together.... but even so.. I would think that it would take very little force applied against the mast to break those spacers free. I'm not positive that the 240 even has those spacers, but I know most of the 25s did.
I don't know..... I'm stumped as to an answer!
Just a few of my past OOPS! moments...... I stepped the mast on my DS II a couple of years ago only to realize after it was up (mast steped through the deck and will stay up without rigging, can't sail that way though) that I'd forgotten to untie al lthe little line that held the rigging to the mast while the mast is unstepped...... and the last little line was just out of reach! Luckily I got it untied somehow with a boat hook. On out old CAL 21 we had to be sure that the backstay didn't snag the mainsheet cleat as the mast piovted up, or we couldn't get the mast all the way up plus it would bend the turnbuckle. I could mention the story of the boat owner who stowed his mooring buoy in the cabin of his boat for the winter, worked fine until he stepped the mast and couldn't get the buoy past the mast to get it out of the cabin! oops!