LDTAGS.EXE is a program that extends the DEU error checker. It
searches a Doom 1 or 2 wad for occurrences of linedefs that have 
functions assigned but no sector tag - a situtation that usually 
causes the game to crash - and can be difficult to locate. The
syntax is simply "LDTAGS wadname.wad". The linedef numbers in error
are reported. Use Alt-S, J in Line mode in DEU to locate them.