What version of the Profile Manager plugin do you have installed? I guess you need to upgrade to the latest release (7.0 ?) before you can use it in Elgg 1.8. It might not show up in the plugin list in case you still have an older version installed because the manifest file is no longer compatible with Elgg 1.8.
Btw. it would be perfectly okay if you would add your question only to 1 thread and not to several different threads.
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