I seem to be having problems installing modules. I can deploy them from the online repository and they usually then appear in the list of installed modules - but they are not available to install onto a page. I've tried for two days and re-installed DNN6 (twice), upgraded to 6.1.2 and  tried every option I can think of but am still just left with the standard HTML module in the "Common" modules and no new modules available in the other module categories.  

Thank you for you help Sebastian,

I am beginning to suspect that the problem actually lies with the Plesk DNN Application install. While a module might install without errors the installed module only appears in the host list of installed modules once and then dissapears - it never appears in the admin list and never appears in the lists of modules available for installing at the page level - so it's difficult to check or edit module settings. One exception to this was the iframe module which did install and is working.. However I've installed the latest DNN directly on another domain (not using Plesk) and this new installation seems to be behaving more as one would expect. I'm not certain that the problem is resolved yet but the gap between bewilderment and confidence is narrowing! Thanks again :-)  Ken

That's true.. I've had problems with Plesk in the past and it's easy to jump to conclusions! A second fresh install just now of the latest version 6.1.2 on yet another domain and all is well with it also, whereas three previous installs that were upgraded from 6.0.0 all had this problem. It's comforting to know that wise advice is available here - thank you again Sebastian. Ken