Would help if you told us something about the files that won't work. File type, format, codec... otherwise, we could sit here all day and guess what's wrong. ;-)
Locate the file(s) within DVD Architect's Explorer window, right-click, and choose Properties. Copy what you see there and post it here.
Folder: C:\Documents and Settings\Owner\My Documents\Downloads
Type: Video for Windows
Size: 563.31 MB (576,829,512 bytes)
Created: Sunday, October 24, 2010, 3:15:29 PM
Modified: Sunday, October 24, 2010, 4:49:30 PM
Accessed: Monday, October 25, 2010, 12:48:27 AM
Attributes: Archive
ACID information
ACID chunk: no
Stretch chunk: no
Stretch list: no
Stretch info2: no
Beat markers: no
Detected beats: no
Other metadata
Regions/markers: no
Command markers: no
Media manager
Media tags: no
Plug-In
Name: aviplug.dll
Folder: C:\Program Files\Sony\DVD Architect Studio 4.5\FileIO Plug-Ins\aviplug
Format: Video for Windows
Version: Version 1.2 (Build 8071)
Company: Sony Creative Software Inc.