Any ideas where to dig from when every extension install is ending to this:

UPLOAD EXTENSION PACKAGE

 There is absolutely nothing in the error log. Another site ( same version ) at the same server installs just fine.
What I can imagine, there must be some differential in web.config, but what to look for? 

This same error occurs what ever I try to install. 

BR: Jarmo

Thanks for the tip. There surely are LOT of logs there....   I just might be too dummy to understand these:

2017-11-10 00:58:15,413 [windflower][Thread:219][ERROR] Dnn.PersonaBar.Library.Controllers.PersonaBarController - System.ArgumentNullException: Value cannot be null.

Parameter name: type

   at System.Activator.CreateInstance(Type type, Boolean nonPublic)

   at System.Activator.CreateInstance(Type type)

   at Dnn.PersonaBar.Library.Controllers.PersonaBarController.GetMenuItemController(MenuItem menuItem)

2017-11-10 00:58:15,413 [windflower][Thread:219][ERROR] DotNetNuke.Framework.Reflection - Dnn.PersonaBar.SiteImportExport.MenuControllers.AdminMenuController, Dnn.PersonaBar.SiteImportExport

System.IO.FileNotFoundException: Could not load file or assembly 'Dnn.PersonaBar.SiteImportExport' or one of its dependencies. The system cannot find the file specified.

File name: 'Dnn.PersonaBar.SiteImportExport'

   at System.RuntimeTypeHandle.GetTypeByName(String name, Boolean throw , Boolean ignoreCase, Boolean reflectionOnly, StackCrawlMarkHandle stackMark, IntPtr pPrivHostBinder, Boolean loadTypeFromPartialName, ObjectHandleOnStack type)

   at System.RuntimeTypeHandle.GetTypeByName(String name, Boolean throw , Boolean ignoreCase, Boolean reflectionOnly, StackCrawlMark& stackMark, IntPtr pPrivHostBinder, Boolean loadTypeFromPartialName)

   at System.RuntimeType.GetType(String typeName, Boolean throw , Boolean ignoreCase, Boolean reflectionOnly, StackCrawlMark& stackMark)

   at System.Type.GetType(String typeName, Boolean throw , Boolean ignoreCase)

   at System.Web.Compilation.BuildManager.GetType(String typeName, Boolean throw , Boolean ignoreCase)

   at DotNetNuke.Framework.Reflection.CreateType(String TypeName, String CacheKey, Boolean UseCache, Boolean IgnoreErrors)

WRN: Assembly binding logging is turned OFF.

To enable assembly bind failure logging, set the registry value [HKLM\Software\Microsoft\Fusion!EnableLog] (DWORD) to 1.

Note: There is some performance penalty associated with assembly bind failure logging.

To turn this feature off, remove the registry value [HKLM\Software\Microsoft\Fusion!EnableLog].

-------------------------------------------------

There are several of identical messages like this after I tried to install with different modules.

Can someone shed a little light to what's going on here?   ;) 

BR: Jarmo