There appears to be a problem with some codecs (which ones yet are undetermined) which can cause any program that accesses the AVI file for property information to go into an endless loop.
The Opus movie plugin can suffer from this, so if you deal with a lot of AVI files that trigger this problem you probably want to disable the movie plugin from Preferences.
Also, the system DLL shmedia.dll which on Windows XP is used by Explorer to obtain property information for AVI files is also affected by this problem.
Opus does not use this file directly, but it is possible that Opus will end up invoking it indirectly when it attempts to retrive generic, non-movie property information for AVI files. That is, it can still cause a problem in Opus even if you have the movie plugin turned off.
This can manifest itself as Opus suddenly consuming 100% of the CPU when you move the mouse over an AVI file, or when you add the Description column to a Lister. Additionally, the AVI file may then be locked, unable to be moved or deleted.
There is more information about this problem in this thread.
We will take steps to prevent this DLL being called by Opus in a future version. In the meantime, if you find this problem occurring you can workaround it by following the steps in the thread linked above:
The underlying problem however is caused by a buggy codec. We are currently researching possible solutions to this.