We have a client who experiences a random error with the details below from event viewer. Of course the dll is there and the system works, just randomly that error appears and restarts the web application.

I actually copied the errors from http://forums.asp.net/p/1496095/3529834.aspx because I have just screengrab from our client and the error is exactly the same, so we are not the only one experiencing it.

Thanks Petr

01.Event Type: Error
02.
03.Event Source: ASP.NET 2.0.50727.0
04.
05.Event Category: None
06.
07.Event ID: 1334
08.
09.Date: 11/24/2009
10.
11.Time: 10:37:32 AM
12.
13.User: N/A
14.
15.Computer: MSN008
16.
17.Description:
18.
19.An unhandled exception occurred and the process was terminated.
20.
21.
22.
23.Application ID: DefaultDomain
24.
25.
26.
27.Process ID: 5308
28.
29.
30.
31.Exception: System.Runtime.Serialization.SerializationException
32.
33.
34.
35.Message: Unable to find assembly 'SD.LLBLGen.Pro.ORMSupportClasses.NET20, Version=2.6.0.0, Culture=neutral, PublicKeyToken=ca73b74ba4e3ff27'.
36.
37.
38.
39.StackTrace: at System.Runtime.Serialization.Formatters.Binary.BinaryAssemblyInfo.GetAssembly()
40.
41. at System.Runtime.Serialization.Formatters.Binary.ObjectReader.GetType(BinaryAssemblyInfo assemblyInfo, String name)
42.

If you use a load-balanced environment, make sure the files are identical. Also make sure that the temporary files for asp.net (in the microsoft.net folder in c:\windows) doesn't contain a different file.

it's still strange though. I found a couple of the same errors on google but with different dlls, and no answer.

Is there any pattern to recognize in the errors at all? I.e. does it occur after the session expires? On a page which contains an LLBLGenProDatasource(2) control?

Looking at the forums.asp.net thread, it looks like it happens when the appdomain is recycled. When you browse the site, and force a recycle in IIS admin, do you see the error happening? (e.g. when you browse a page with data bound through our datasourcecontrol, so entities are serialized into the viewstate/session etc. )