If a user is able to connect and set up a TCP session with an application server, but the application does not function otherwise, or function correctly, then, there are a number of areas that can be investigated. These areas can be investigated using a combination of packet-level analysis, error reports, and configuration comparisons with captures and configurations from other users' machines:
User credentials: The most common reason for specific-user issues with application functionality is the lack of proper credentials, authorization, rights, and so on. This is the first thing to check whether other users are working normally.
Application settings on the user machine: Some applications require specific configuration files to be placed on a user's machine in a specific location. Applications may also require certain version levels of application-specific utilities, Java, .NET frameworks, and so on. Usually, an application will provide an error message...