This looks like a known issue with PI WebParts 2013: PLI 101418
Basically, you need to re-add the following string in the web.config files:
<serviceHostingEnvironment aspNetCompatibilityEnabled="true" />
Where to put this config?
The default directory is c:\inetpub\wwwroot\wss\VirtualDirectories\80\web.config
But that bug affects all SharePoint application web.config files, so you might want to check web.config files for all other Sharepoint sites.
These files directories can be found with IIS manager: do a right-click on the SarePoint site->Manage Web Site->Advanced Settings->Physical Path
it works now.
thank you very much for your support.