The latest Diablo II patch made some alterations to the structure of the game files, which slightly changes the downgrade procedure.
Here is how to downgrade your game back to 1.13c, necessary in order to play on our realm:
1. Download the archive 1.13c Downgrade Files
2. Extract ALL files to your Diablo II directory, confirm overwrite when prompted
Now you are good to go.
Maphack doesn't work if you use this method. We are investigating a fix.
NB: Your Median characters (if you don't use D2SE) were moved to C:\Users\YOUR_USERNAME\Saved Games\Diablo II. To get them back, create a folder called "Save" in the Diablo II directory and move all the contents over.