hi 

my customer has been using gallery module for several months,but suddenly today he has gotten this error :

i check the events and i saw this :

ModuleId: -1
ModuleDefId: -1
FriendlyName: 
ModuleControlSource: 
AssemblyVersion: 5.6.0
PortalID: 0
PortalName: بیمه آرمان
UserID: 1
UserName: host
ActiveTabID: 151
ActiveTabName: گالری تصاویر
RawURL: /دربارهما/گالریتصاویر.aspx
AbsoluteURL: /Default.aspx
AbsoluteURLReferrer: http://www.armanins.com/%D8%AF%D8%B1%D8%A8%D8%A7%D8%B1%D9%87%D9%85%D8%A7/%DA%AF%D8%A7%D9%84%D8%B1%DB%8C%D8%AA%D8%B5%D8%A7%D9%88%DB%8C%D8%B1/tabid/151/ctl/Module/ModuleId/597/Default.aspx
UserAgent: Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/535.1 (KHTML, like Gecko) Chrome/13.0.782.107 Safari/535.1
DefaultDataProvider: DotNetNuke.Data.SqlDataProvider, DotNetNuke.SqlDataProvider
ExceptionGUID: 0a2d0c58-5882-492c-9160-5974d12e0cf7
InnerException: Object reference not set to an instance of an object.
FileName: 
FileLineNumber: 0
FileColumnNumber: 0
Method: DotNetNuke.UI.Containers.ActionBase.get_ActionRoot
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.UI.Containers.ActionBase.get_ActionRoot() at DotNetNuke.UI.Containers.ActionBase.Page_Load(Object sender, EventArgs e) --- End of inner exception stack trace ---
Source: 
Server Name: GATEWAY

 i dont know what is the problem? 

the problem was due to permission, i had been set new application pool for my site and the new user of that application pool didnt have enough permission! and that`s it every thing is ok now :)