object reference not set to instance of object

There are several reasons a worker process may get recycled thus dropping all currently active sessions. An application has to cope with sessions being dropped. Anything that needs to have a life time that exceeds a possible session should be stored in a DB. Sessions are meant to be used for storing temporary stuff for convenience only.

(Eventhough you can tune the values for the automatic recycling of the worker process, it can still happen that an iisreset is issued on a machine (after an 'wlbs suspend' perhaps) causing it to instantly loose all session state, unless your using an asp state session server hooked up to a MS SQL Server.)

Start Modification:
Just found this on I found this on http://www.xefteri.com/articles/show.cfm?id=14 :

<processmodel>
timeout="168:00:00"
...

The first involves the timeout attribute, which simply creates a new process after the amount of time specified as a value. For example, the above setting will automatically start a new process after 168 hours, or one week. The time clock starts right after the first request is made, because the process is actually created when the first request to the ASP.NET engine is made. This setting can be extremely useful in scenarios where there is a slow leak in memory and performance, and periodic IIS resets are needed.

1 ...
2 <processModel
3 requestLimit="10000"
4 ...

A second way is to use the requestLimit attribute and give it an Integer value. A value of 10,000 like above, will start a new process after 10,000 requests have been made. This can be useful if our web server's performance degrades after a set number of requests, instead of simply some amount of time past.

1 ...
2 <processModel
3 memoryLimit="50"
4 ...

A third way is to let your system watch how much memory the process is consuming. In the above example, the attribute memoryLimit is set to 50, which means that if the process uses more than 50% of total system memory then the process is killed , a new one is created and all existing requests are reassigned to the new one. This is extemely helpful is cases where a memory leak is present, no matter how slow the leak is.

1 ...
2 <processModel
3 responseDeadlockInterval="00:03:00"
4 ...

A fourth way of doing this is by using the responseDeadlockInterval attribute. The time setting above of 3 minutes will restart the process if two things happen: there are requests in the queue, but there have not been any responses for the last 3 minutes.

1 ...
2 <processModel
3 pingFrequency="00:00:30"
4 pingTimeout="00:00:05"
5 ...

The fifth and last way of recycling the process, is to use the pingFrequency and pingTimeout attributes in conjunction. The system pings the ASP.NET process at the pingFrequency interval, and restarts it if there is no response within the pingTimeout time interval.

End Modification


Cheers

Manfred

As you said, which session mode you are using.If inProc then add the line

<sessionstate mode="InProc" timeout="60"></sessionstate>

in config file.

Also, before accessing any value from session, put a null check, because a session can be destroyed by many reasons. So to avoid YSOD, have a null check, show some error or redirect to some other page if required.

You need to check the session before assigning the value. because session may expire after 60 mins. so if u click after 60 mins u will get this error.

So check the session linke,

if(session["projectname"] != null)