First of all, the problem with The Den is rather known issue with 1.01. The only way to solve it is to update the game, as you have already done. But, as you probably are in the very beginning of the game, I suggest you patch the game up to 1.04 or 1.05, as the 1.02 version is still very buggy and can make several aspects of the unplayable or unusable.
Secondly, even though the converter usually works pretty well, there is a chance that the save converted become somewhat corrupted, ending up to make the game even more buggy or even making the game disallow saving again. So, as you are probably at the beginning of the game (first time visiting The Den, right?) I suggest you just start over with patched game.
Lastly, it's very good idea to use all slots and not just one. One method is saving to new slot every time you visit new city, and dedicate that slot to the specific city. In further game, this may save you loading too far away. Also, as there is only 10 slots for saves, it's good idea to backup the older saves to different location to be able to free older slots for new cities. One folder structure for backups is following:
- Under the main folder, create new folder called "Backup"'
- Under the "Backup" folder create new folder for every character you are playing (if you have more than one). This allows you to have several characters simultaniously, and easy access to them every time you want to switch between characters
- Under the character folder, copy the save slots folders, and rename each folder to indicate what city/town/place it refers
Every time you visit new city and make the new save for it, you just copy the slot to the character folder and rename it. Use two or three first save slots for general saving, and backup them as well regulary to the backup folder under the character name. With general saving slots, cycle through them when saving, for example 1 slot -> 2 slot -> 3 slot -> 1 slot etc.
When you want to reload older save from the backup, just copy the renamed folder to the save folder, then rename it to the save slot you want it to replace, for example "Slot 10" (sorry, can't recall at the moment how the folders are exactly named under the save folder, but you can figure it out from the other slot folders there), and voilá, you backup shows in your saved games list. Just remember to shut down the game when doing any copying, especially when copying backup back to the game.
So, basically your character's backup folder could look like following:
- General 1
- General 2
- General 3
- Arroyo
- The Den
- Klamath
and so on...
You can modify the backup folder structure to your like, perhaps saving after every level or two, and rename the slots according to your level? Which ever suits you best, the basic idea is the same, and highly recommended.