The Decal file named memlocs.xml is now encrypted (as of the October 2003 patch).
All versions of ACTool up to and including version 4.4.15 do not work with an encrypted memlocs.xml.

The most common ACTool error received is "Could not find ItemBusyGUID in MEMLOCS.XML"

There are 2 possible solutions.

1. Get the latest 4.5.x beta of ACTool
2. Find a plugin author who will generate an un-encrypted memlocs.xml for you

Recommended option is #1. 4.5.4 beta