I'm pretty sure that this is what was a supposed bug even years ago.
If I don't get wrong is all related to gathering all objects otherwise bridge won't rise enough.
It's strange because you say you followed a walktrough, but I already heard about this bug even years ago (and was no bug, simply you can commit actions that preclude you from having all right items like with the bonding plant).
And you can discoer this only later, when the only option left is to restart.

I remember back then people with the CD version going on and on about this... I had the floppy version and didn't run into it.

Ok now I'm not going to claim that the floppy version is the end all be all, but I've won the floppy version a long while back...

I bought this as I wanted a 'better experience' than the floppy version and to show my support although I've got CD's for MAC & PC and I still have my original floppies!!... But you'd think i'd have saved some save games.

I recently finished RTZ and didn't run into this problem, but I did patch the game to version 1.2 (I think the GOG version is 1.1) and I also played in Scummvm, so one or both of these might have fixed the problem.

I've finished Return to Zork numerous times over the years, and I've never run across this problem. I do have a vague memory of having to go back for more hay or something, but I was able to do that and progress. I'd suggest making absolutely sure you didn't leave anything lying around anywhere....

While we're on this topic, I'll say what we're all thinking - this particular "puzzle" really is stupid :D Someone at Infocom would be hard-pressed to explain the functionality of this bridge...

I haven't tried this again since my original post but I do know that I went back for hay, and did everything I could, knowing from the start of the game to keep and collect everything and doing exactly that. I even got a list of all of the items that get thrown in and had them all and still didn't get the bridge to get high enough. I eventually also just watched the last bit on youtube.

i had the same problem..I tried going back to the cow and take more hay ,more carrots and meat from the farm ,bat guano and more money(which did not appeared when i striked the tree with the sword).The bridge almost got to the proper level but i probably needed 1-2 more items but i could not get more hay or meat or carrots or bat guano so i ended too watching the ending in youtube.

In any case maybe more money mean more weight ? Or when you are in the bottled ship use the mirror instead the shiny metal plate which needs the rag to get shiny...?

In any case as this is the normal cd version ,it is not actually the ultimate,REELMAGIC one with the full motion videos and more animated backgrounds,i hope GOG tries to make that version work along fixing this problem (if it is fixable).

I ran into this glitch last night, and again this morning after I loaded an earlier save to get back the rag, which the walkthrough I was following said was a required item to complete the bridge section. What I found was that having all of the items required, and more in one case, did not actually give me a better chance at completing the bridge section. I did eventually take a different approach, which lead me to successfully cross the bridge. Some of the things I was reading online about passing the bridge section stated that it was possible to pass the bridge section without having all of the items stated as required in the walkthroughs, which lead me to the theory that the bridge was only counting on me throwing everything I had in my inventory, regardless of the amount.

*SPOILERS BELOW*

To get around the glitch, I actually tried to minimize my inventory by using up items that would respawn themselves after each use, but not after being thrown into the bridge. The rag that I had previously brought back with me from an earlier save, I decided to use it to shine the metal thing, which removed it from my inventory. I also used up the hay and carrots in my inventory. I did not try to use up my zorkmids, which I think I could have done, and then replenished from the tree, but lucky for me I didn't have to. I started the process of throwing my minimized inventory into the bridge until I had nothing left. I found that I got very close to raising the bridge, about the same spot that I did with the maximized inventory, so I headed out to get the extra carrots and hay. I noticed that another steak had spawned at some point in the refrigerator, but I decided not to grab it unless this next attempt was not successful. I warped back to the bridge, threw the hay and carrots into the bridge, and was happy to see that the bridge was finally safe to cross.

One additional thing that I did, that I don't think really made a difference, was to go into the inn and stay for a night, which I had skipped completely due to the walkthrough leaving that part out. I got some extra points and a nightmare dream sequence to watch, which made it worth it enough, but it should be noted that there were no additional items to pick up there.

I hit this glitch, and piecing togehter poieces from this thread and a few others, it looks like the amount the bridge needs thrown at it is proportional to the size of your inventory when you go there. I dumped half my inentory outside the citadel before going in, threw all that was left at the bridge, then went back, picked up a few pieces from the ground, threw them, and it was raised, and I still have over a dozen unthrown items.

I tried several times with a full inventory, with going back and getting guano, hay, carrots, throwing the mice and the box separately etc, and couldn't get it up.