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this is just a guess, but as it happened to me before, i might be right. if i´m not, don´t kill me
maybe it´s a "folder in the folder"-problem? make sure you have the module folders (admin, language etc.) directly in the xoops-chat folder, and not another xoops-chat-folder in it. this sometimes happens while expanding the archive (at least it does to me!) and then transfering the wrong folder-structure...