Recently i installed the forum module on my new child portal.
This is the first time i try to upload an Avatar.

I guess i didn't set rights correctly, but i don't know the folder to set rights on and how the should be.
Can u guys please tell me where to set rights or else explain how i can make it possible to upload avatars.

The stack trace in the exception below is not explaining much, since it gives an standard null reference error "Object reference not set to an instance of an object".

ModuleId: -1
ModuleDefId: -1
FriendlyName: 
ModuleControlSource: 
AssemblyVersion: 5.1.0
PortalID: 4
PortalName: De Piaggio MP3 Club Nederland
UserID: 6
UserName: rfcdejong
ActiveTabID: 111
ActiveTabName: Forum
RawURL: /dotnetnuke/Forum/tabid/111/ctl/UCP/mid/433/language/nl-NL/Default.aspx
AbsoluteURL: /DotNetNuke/Default.aspx
AbsoluteURLReferrer: http://www.piaggio-mp3.com/dotnetnuke/Forum/tabid/111/ctl/UCP/mid/433/language/nl-NL/Default.aspx
UserAgent: Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US) AppleWebKit/530.5 (KHTML, like Gecko) Chrome/2.0.172.39 Safari/530.5
DefaultDataProvider: DotNetNuke.Data.SqlDataProvider, DotNetNuke.SqlDataProvider
ExceptionGUID: 072a3f6d-6ddc-43ee-930e-bd4903476b67
InnerException: Object reference not set to an instance of an object.
FileName: 
FileLineNumber: 0
FileColumnNumber: 0
Method: DotNetNuke.Security.Permissions.PermissionProvider.CanAdminFolder
StackTrace: 
Message: DotNetNuke.Services.Exceptions.ModuleLoadException: Object reference not set to an instance of an object. ---> System.NullReferenceException: Object reference not set to an instance of an object. at DotNetNuke.Security.Permissions.PermissionProvider.CanAdminFolder(FolderInfo folder) at DotNetNuke.Common.Utilities.FileSystemUtils.UploadFile(String RootPath, HttpPostedFile objHtmlInputFile, String NewFileName, Boolean Unzip) at DotNetNuke.Common.Utilities.FileSystemUtils.UploadFile(String RootPath, HttpPostedFile objHtmlInputFile, Boolean Unzip) at DotNetNuke.Modules.Forum.AvatarControl.cmdUpload_Click(Object sender, EventArgs e) --- End of inner exception stack trace ---
Source: 
Server Naam: WIN64

Thanks, it solved my problem.
Anyway the exception was unclear about this and that should be an new issue / workitem on low priority :)