Why would some NPCs not work when I run VIS?

I'm working on a single-player map for HL2. When I run just a BSP
compile to test whether my npc's are working, all the npc's (primarily
Combine soldiers and manhacks) work perfectly. However, when I
run a full-VIS compile, certain groups of npc's no longer function
properly - instead of going to their correct assault points and/or path
corners, they wander off to other places. I don't understand why
a VIS compile would cause them to do this - does anyone have any hints
or suggestions.

I've run the BSP compile and tested the map several hundred times and
it works perfectly EVERYTIME. And I run VIS and certain groups
quit working EVERYTIME. I've tried moving the positions of the npc's so
that they spawn closer to their path corners or assault points, but it
hasn't helped so far.

Any helpful suggestions would be appreciated.

Thanks,

Drew

its likely an issue with your info_nodes. try typing "ai_show_connect"
in the console, which will draw green lines between linked nodes and
red lines where nodes tried to link but failed. if there isnt a decent
green path to where you want the soldiers to run, they arent gonna do
it properly. this might also show you where your problem is so you can
fix it quickly...

hope that works...