ActiveMovie Window message???

Question

I hope someone can help with this. I've been working on it for 3 days and I'm at my wits end. I've searched the problem on the forum, the Adobe site as well as generally online using 3 search engines.
I have a large DL9 project that has been humming along beautifully for 6 months. After burning it to DVD for presentation in June, I've just been making minor changes and tweaks to some of the menus, and have been replacing audio tracks in some of the timelines as they've been provided to me by my partner after final mix. Essentially the project was finished except for replacing the audio files with the new mixed files.
So Friday morning I imported a few .wav files, deleted the old .wav files from the timelines, deleted them from my project and placed the new .wav files where they belonged. A procedure I had done before. So then I started getting a message that said "Sorry an internal engine error has been detected. Please save your project with another name and restart." Then it locked up and wouldn't let me save.
I searched that problem and found a very helpful thread here on this forum about how encodes made with Procoder produce this message. A couple of weeks ago I installed a Canopus program that allows a computer that does not have Canopus/Procoder to play Canopus files. I needed it to open some Premiere projects that had been created using Canopus. So I deleted the Canopus program but it didn't help. Then I discovered I only got this message when I played a specific timeline (actually the timeline would play fine with just the .wav, it was the .mpg that it wouldn't play). I deleted the timeline and the "internal engine error" message has not reoccured, however, the project is 4.5 hours long so I haven't played everything all the way through.
So now when I open the project I get a box that says "ActiveMovie Window: Adobe Encore DVD.exe - Unable to Locate Component." Then it says "This application has failed to start because AdavAudioDec.dll was not found. Re-installing the application may fix this problem." When I close that box, two more pop up, and after I close them the project loads. It works but behaves oddly.
Subsequently I repaired Encore, no help. So I uninstalled it and reinstalled it. No change. I created a new Encore project using some of the elements from the project and it plays fine. (Note that the problem project is on an external HD, but the new project I created is on my C drive.)
So then I restored a backup of the project from 2 months ago and it has the same problem. So this made me think the problem was in the folder with all of the encodes, since the project is using those files. So I renamed that folder so Encore couldn't find it and loaded the project but got the same message. So it appears it is loading something that needs this driver, but I cannot figure out what it is, or locate the driver.
I am really lost and confused now and have no idea what to do next. My system is a P4, Windows XP Home. One other thing that's new: I purchased a DLT 4000 and a PCMCIA SCSI Adapter that I installed a week ago, tested and put aside for use later in the month. It did not require any software installation.
Julie

Answer 1

Jeff, your explanation makes sense and it helps to understand what is likely going on. I reinstalled the decoder first and searched for the .dll and didn't find it. So I reinstalled the program that allows my system to play Canopus files and searched again and still didn't find it. However, my Encore project opened without the messages popping up. So I uninstalled just the second "play only" program and boxes popped up again. I still think you're right about the decoder thought and here's why.
I installed the decoder (converter) in December, not long before I started building this project. During the build of the project, I used 3 different .avi files as motion menus that were created on my partner's system that uses Premiere and Canopus. I cannot remember if I used the converter on those files to change them to Microsoft .avi's before incorporating them in the project, but regardless it seems apparent that the decoder program is needed on my system for Encore to be happy with those files. When those pesky ActiveMovie windows pop up, I get exactly 3 of them every time.
As a test, I think I will try using the converter to change those 3 files to Microsoft .avi's, uninstall the converter, and see if I still get the messages. If I do, then I'll assume what you explained about the codecs and just keep the converter on my system.
My worry though is all this started with an "internal engine" error from Encore that would occur at a specific frame in one of the timelines. I'm concerned that the Canopus stuff is conflicting with Encore and corrupting the project. I was not having any problems with that timeline before and had successfully burned the project for presentation in June. So something happened to that file since then. Hopefully I'm wrong and it was just an isolated case of a file getting corrupted for some other reason.
Before I do anything else though I'll try your suggestion with changing the Video Playback checkbox. Thanks Jeff. You've been the calm in the storm and a big help!