ok unlike every 1 els , i know how you feel i had same problem 3 weeks ago....
you must get the wadmanager.wad file , just look it up off google , but you might not find tnhe version you want, im currently using 1.0..... 1.3 and 1.4 dident have wads i can find and i had a code dump error in them .....
so search goole for wadmanager.wad and install it using itself -.-