I am having the same issue, I'm still looking into it to make sure it's not our website but it is looking more and more likely to be the session provider.
I can't find any bug reports relating to this issue, we are using 6.2.2.0 of the provider. It's not a massive site, but is still fairly busy (3,000 users per day) and we are getting this logged between 3 - 20 times a day.
My interpretation of the first report was that when this happened the whole site was unresponsive and you had to restart the application pool, I might have understood them wrong but this isn't the case in my environment.
When it happens the individual user (that the session belongs to) is stuck and receives that error on every page but all other users of the site are fine. If the user with the session problem closes the browser and re-opens it (getting a new sessionID) they are then able to use the site again.
Here is a copy of the stack from our exception logging class
Event code: 4015
Event message: An unhandled exception has occurred.
Event time: 18/03/2010 09:42:06
Event time (UTC): 18/03/2010 09:42:06
Event ID: 9c02c905c0bb4abc9d8a623d056183c8
Event sequence: 3259
Event occurrence: 34
Event detail code: 0
Application information:
Application domain: /LM/W3SVC/2/ROOT-1-129133763291120883
Trust level: Full
Application Virtual Path: /
Application Path: C:\Sites\xxx\htdocs\
Machine name: WEB2
Process information:
Process ID: 2396
Process name: w3wp.exe
Account name: NT AUTHORITY\NETWORK SERVICE
Exception information:
Exception type: SqlNullValueException
Exception message: Data is Null. This method or property cannot be called on Null values.
Request information:
Request URL:
http://xxx/xxx/page.aspx
Request path: /xxx/page.aspx
User host address: xxx.xxx.xxx.xxx
User:
Is authenticated: False
Authentication Type:
Thread account name: NT AUTHORITY\NETWORK SERVICE
Thread information:
Thread ID: 15
Thread account name: NT AUTHORITY\NETWORK SERVICE
Is impersonating: False
Stack trace: at MySql.Data.MySqlClient.MySqlDataReader.GetFieldValue(Int32 index, Boolean checkNull)
at MySql.Data.MySqlClient.MySqlDataReader.GetInt32(Int32 i)
at MySql.Web.SessionState.MySqlSessionStateStore.GetSessionStoreItem(Boolean lockRecord, HttpContext context, String id, Boolean& locked, TimeSpan& lockAge, Object& lockId, SessionStateActions& actionFlags)
at MySql.Web.SessionState.MySqlSessionStateStore.GetItemExclusive(HttpContext context, String id, Boolean& locked, TimeSpan& lockAge, Object& lockId, SessionStateActions& actions)
at System.Web.SessionState.SessionStateModule.GetSessionStateItem()
at System.Web.SessionState.SessionStateModule.BeginAcquireState(Object source, EventArgs e, AsyncCallback cb, Object extraData)
at System.Web.HttpApplication.AsyncEventExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute()
at System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously)
Custom event details:
Edited 2 time(s). Last edit at 03/18/2010 04:42AM by Steve Hammond.