If you are working on the master file, you MUST have all of the current static mesh files working properly in the level. If for some reason you're getting errors about missing static meshes and you save the master file anyway, you will break all of the correct links to the mesh package and everyone will now have a broken file, even if they have the correct mesh packages on their computer.
My suggestion is that we all start using the default folder that UT3 looks to for custom mesh packages:
C:\Documents and Settings\USERNAME\My Documents\My Games\Unreal Tournament 3\UTGame\Unpublished\CookedPC
Note that "USERNAME" should be replaced by whatever your user name is on Windows.
For instance, on my computer it looks like:
C:\Documents and Settings\Heather\My Documents\My Games\Unreal Tournament 3\UTGame\Unpublished\CookedPC
Dump all current mesh packages into this CookedPC folder, NOT within CustomMaps or any other sub-folders within CookedPC.
When you load up the level from now on, you will not have to load the mesh packs first, since the mesh packs are in the default folder UT3 looks in. Keep in mind that if for some reason there are any additional changes to the mesh packs, you will need to dump the updated mesh packs into this folder again (and overwrite the old ones.)
In closing, PLEASE remember that if you're seeing mesh errors when you save the file, you're making those errors happen for everyone else.
Avoid making problems that can be avoided.
Thanks!
If you have any questions, launch them at me.