You didn't say what version Photoshop, or what version of Windows, but no hits for ADM or ADMplugin.apl or similar in Adobe KB, but Googled from another site:
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"In order for Photoshop to run any plugins, it must have a file called ADMPlugins.APL installed. This is a standard Photoshop file and for some reason Photoshop will forget where it is. This file must be present on the hard disk in the following folders: (Note - many people install Photoshop under Program Files and then the Adobe folder.)
In PS5.5, 6.0, & 7.0 the file ADMplugin.APL must be in: Adobe/(Photoshop Folder Name)/Required.
In PS5.0 the file ADMplugin.APL must be in: Adobe/Photoshop50/Plugins.
If at this point the program still does not recognize the Plugins or does not find the ADMPlugin.APL file you will need to Re-Install Photoshop." ========================
In my PS 7, ADMPlugins.APL is indeed in:
C:\Program Files\Adobe\Photoshop 7.0\Required
Do you see the file in YOUR folder list in Required?
If so, or if not, is still a mystery as to why it's either not being installed or if installed, is not seen.
Maybe an UNinstall first, and also make sure Adobe Photoshop directory structure is completely gone, including folder structure containing prefs, which is not deleted with uninstall:
http://www.adobe.com/support/techdocs/6712.htm Also, delete all temp files, reboot. Try re-installation.
Just sort of guessing here, I think this is first time I've ever heard of this prob, and didn't even know that the ADM thing was part of PS until this thread.
Mac