You can have both version of the game in PC and for imba map you need 1.26.
If you don't have 1.26 patch because you already have 1.28.x and version switcher failed to restore it, or if other login clients corrupted your w3 files, or you tried hax , or just your game has been installed form long time ago, now you need a fresh copy of Warrcarft III.
Warrcarft III English version 1.26 with PVPGN support to connect at INGAME realm and others.
Download all 3 parts and move them in in partition C. Extract Warcraft III.zip archive . Warcraft III folder is created.
When you extract right click only on Warcraft_III.zip and "Extact here". Do NOT select all archive and extract.
Then find and run in Warcraft III folder the registry file named Realms6.reg. Now you added the PVPGN realms.
Now run the game from "Start GAME w3l.exe" press Battle.net and connect to default INGAMERO realm.