WARNING: This process involves editing the Windows registry, so if you are squeamish about that sort of thing, do not attempt this. I'm not responsible for broken computers, hurt feelings, or terrified household pets.
I've ocassionally run into an issue since CS4 where certain plugins/effects would spontaneously cease loading in Premiere Pro and functioning, and it apparently continues to affect CS5. This happened on three total different computers, so I'm not sure what the underlying cause is. There was no clear reason why this would happen: I'd use the effect one day, come back the next and load my project, and the effects would be reported as "missing" upon project load:
This doesn't happen with the "built-in" effects that ship with Premiere, but it has happened repeatedly with the Cycore effects (copied from the AE plugins directory) or with third-party plugins like those from DigiEffects, Red Giant, Trapcode, etc. After this loading mesage, the instance of the filter would show up in the Effects Control Panel as "Offline Filter" and the filter would have no effect on the clip to which it is applied. This isn't a case of the effect simply not being compatible with Premiere, as they had previously showed up in the Effect bin and could be applied and used, as evidenced by the error pop-up above. Uninstalling and reinstalling the plugins has no effect on correcting the issue. After a bit of hunting around, I finally figured out how to correct the problem--not the underlying cause, which I still cannot pinpoint, but I can at least get the filters/effects/plugins loading and operating again. Note that the following applies to Windows systems; I'm not sure if this affects Macs, and if it does, I have no clue as to how to correct it.
In Explorer, go to the following folder: C:\Users\username\AppData\Roaming\Adobe\Premiere Pro\5.0. Inside, you will find a file called Plugin Loading.log. This is simply a text file which you can open with Notepad or a similar text editor. In it, you'll find a long list of entries like this:
Anything that says "The plugin was successfully loaded from the registry" was obviously successfully loaded, and therefore able to be used in Premiere. However, upon scrolling through the file, you will see something like this (using the CC Snow example from above):
At some point in the list, the successfully-loaded plugins will stop and the list will change to "The plugin is marked as Ignore, so it will not be loaded." Herein lies the problem and the solution; we need to correct this issue in the registry, since we know from the above example that the plugins are loaded from the registry.
In Windows, click the Start button/orb, and select Run; in the panel that appear, type in regedit. This will launch the Registry Editor. A good safety precaution before going any further is to select File > Export and save your ENTIRE registry by selecting the All radio button. Pick a location and back it up; it may take a few moments. This is important to do if you're not familiar with editing the registry, because you can pretty quickly toast your OS installation if you poke at animals you shouldn't. You've been warned.
Navigate to the following key in the Registry Editor: HKEY_CURRENT_USER\Software\Adobe\Premiere Pro\5.0\PluginCache.64\en_US. Here, you will see a long list of other subkeys, each of which bears the name of a plugin. If you click on one of the keys in the left pane (looks like a folder icon from Explorer), you will see a list of values, their types, and the data they hold in the pane on the right. Using the Plugin Loading.log text file as a guide, compare a plugin that loads with one that doesn't. You'll see the following disparity:
If the "Ignore" value is set as "0" (binary data), the plugin loads; if the "Ignore" value is set as "1," the plugin does not load. Based on this information, the solution should be apparent:
Using the Plugin Loading.log text file as a guide, change this data for any "Ignore" value set to "1." An important note: this does not "enable" effects that wouldn't otherwise work in Premiere Pro anyway. For example, some of the Cycore effects, like Time Blend, Time Blend FX, and Split 2, do not work in Premiere, regardless of how the "Ignore" value is set. If you should happen to change them, Premiere will set the value to "1" the next time you launch the program.
Once you've changed these values (there's no need to save, as the changes are immediately made to the registry), launch Premiere. If you were successfully, nothing interesting will happen--you'll be greeted with no error messages, and your once-missing effects will resume their place and settings on your sequence clips. You can confirm the "fix" by reopening Plugin Loading.log (be sure to have closed this file before relaunching Premiere, as it is simply overwritten each time), and looking for the entries that were previously ignored:
There you have it. Again, I don't know the reason why this happens, but I've been bitten by this oddity numerous times in CS4, and now in CS5. My best guess is that it happens when Premiere crashes during loading (which seems to happen to me) or there is some other "issue" during launch. As a sort of self-defense mechanism, Premiere tells the registry to disable these plugins to ensure a successful load the next time the program is launched, but then they are not automatically re-enabled, and hence the need for this somewhat convoluted fix. Under normal circumstances, I would imagine that relatively few users will ever encounter this issue--but if you do, you now know how to get back to work.