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Yes, the iMenu folder (with xoops_version.php and some other files and subfolders) is all present and correct in the Modules folder on the server. All permissions are set as advised earlier(see top of post).
Well, I got a bit further...
I tried installing the Counter 2.02 module (got it from the repository, here) and that instaled OK. It appeared in the module list and also in my blocks admin menu, (but only after I had selected "webmasters" as the group! That figures)
But once I have set it to visible, my web page comes out as a blank page.