No, so far I have not had this problem. Check out the plugins folder of your Hudson installation. It should contain the hpi file you downloaded and a folder (the same name as the hpi file) with the exploded version. if both are missing, just drop the hpi file into the plugins folder and restart Hudson. It should extract the hpi file.
I looked at the blog post you linked. It mentions that this is a modification of the ext-email module. Check if the optional plugin is installed. If so, uninstall it and check if the hpi file is installed correctly. Just wondering if this could be a version issue (that ext is newer than the groovy -email plugin).
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