couldn't load xul.dll

 Installing successive Firefox versions, 17 functions, 24.8 and 31.8 fail with:

couldn't load xul.dll

 Have gcccore 1.3.1, extra mozilla dll zip, mozconfig runtime and appears all required
dll files.

 Using Pmdll.exe reports firefox.exe as startable, plugin-containers.exe as can not find
xul.dll in libpath.

 Created test.cmd file with:

set MOZ_CONSOLE_LOG=1
firefox.exe  2>&1 1>console.log

 Nothing in console.log

 Machine is Intel P4 2gb ram, kernel is W4 single core, using ECS 2.1 
have: VIRTUALADDRESSLIMIT=2048 in config.sys, no other Mozilla apps.

 Online search usually indicates missing dll but all seem to be in place. Since version
17 operates correctly, something else must be needed for later version.

        Suggestions?

  Cal