Meanwhile, the problem has been solved and as an extra, the option to allow posters that have no email address was added (Business Edition only).

Thanks Rob for Your support,
ok, I'll wait for Your solutions.
regards
ciao
Luigi

Dear Luigi, thank you again for your efforts and info.
I believe that I have identified the problem. In a WAMP localhost environment, the folder/file directory separators used are different form those used in an online website, namely '\' instead of '/'. This leads to a faulty root dir in the WAMP environment so that the required files cannot be found.
In an online (web) application this will not be a problem, EXCEPT that a similar problem occurs when you install the joomla website in a subdirectory, this I learned today. So if you test the module with Joomla! installed on http:/www.domain.tld/ then there will not be a problem, but if you install Joomla! in http:/www.domain.tld/joomla/ then there is again a problem with finding the required files. So my guess is that you have tested in a 'real' web environment using a sub folder for the Joomla! install.
Bottom line, I know where the problem is and I can fix it, which is the good news.
I will need a little bit of extra time and let you know when it is ready. I will probably send you the new install/update package to your email address. Regards and ciao!

sorry for my late answer and thanks for your quick answer.
I have tested also in production environment (provider Aruba in Italy), unfortunally I have no access to server logs but I have a general error message.
It seems to be as the application gets an error path of includes/defines.php and includes/framework.php, giving the error in mod_drop_a_note/tmpl/form_new_unreg.php but also in help and private message, and seemsto be in all routines containing
require_once ( JPATH_BASE .DS.'includes'.DS.'defines.php' );
require_once ( JPATH_BASE .DS.'includes'.DS.'framework.php' );

I don't know if this is usefull for You.
if You need further info pls don't hesitate to tell me
thank You for Your attention
best regards
ciao
Luigi Squizzato

I can confirm the error when using a local machine like XAMP, see attached screen dump.
We will now resolve this issue.

Luigi Squizzato wrote:
Dear Luigi, thank you for your feedback. Your error messages had the directory separator '/' missing, which I have added in above quote.

FIRST: I have just tested the Drop-a-Note Premium module on a standard live J3.6.5 [ Noether ] install with PHP 5.6.29 and MySQLi 5.6.29. There was no error and no problem. I do not know how Joomla! 3.6.5 behaves on a local WAMP server install, but there may be a problem, because...

SECOND: the error notice says that file /includes/defines.php is missing ('No such file or directory'). This is a standard Joomla! file that apparently cannot be found. I think it is unlikely that the file is missing, because it is part of the standard Joomla! install. Please check this.

We always test our extensions on a 'real' development website, i.e. not on in a WAMP environment, because we have seen that websites sometimes behave differently on WAMP compared to the real website.
Nevertheless I will give this module a try on WAMP and report back later on this forum.

If more convenient for you, you may email us on webdesign(AT)innato.nl

Regards