The Asp.net MVC 2 + extjs 3 site sometimes cannot obtain data, resulting in instability.

A oa system is developed using ASP. net mvc 2 and extjs 3 and deployed in Windows Server 2003 and IIS6. Some problems have occurred, making it a little depressing.
 

 
Symptom: Sometimes, after logging on to the OA system every two or three days, the data cannot be obtained. For example, the Child structure cannot be displayed in the tree structure displayed by extjs; the data list cannot be displayed. CheckCodeNo problem was found. You only need to re-release the OA system or restart IIS (using the iisreset command) to restore the system to normal. In addition, the system has fewer users and the access is not frequent.
 

The system has also added a text message cat to send text messages. The data inventory of its database and OA system is placed in an SQL server to send text messages.
 

Also, the application is in the "event manager" of the server.Program. The specific exception is displayed in an indefinite position, but the program does not seem to have seen any specific exceptions.
 

  
 this problem has been plagued for a month, still not solved. Please give your comments