The Jacob DLL
Jacob.jar relies on a DLL file that it loads off of the library path or classpath. This means that you must either copy jacob.dll into your path or use VM options to add jacob.dll directory to the path.
The code is written so that the jacob.dll is only loaded one time per classloader. This works fine in the standard application but can cause problems if jacob.jar is loaded from more than one class loader. This can happen in the situation where multiple jacob dependent web applications run in the same container like a web server or JWS runtime.
In the case of a web server, Jacob is normally put in the application specific WEB-INF/lib directory. This is the "right" way to do it and works in most situations. But, if Jacob is put in the WEB-INF/lib directory of each application's war file for more than one application then a problem occurs. In this situation, the web server uses a different classloader for each applicaiton. This means that each application will attempt to load the jacob.dll and errors are generated. The only way around this at this time (1.11) is to put the jacob.jar in the common/lib because that classloader is inherited by all of the applicaitons so the DLLs will only get loaded once. This problem is described in SF 1645463 and should be fixed in some future release, fix method and time not yet determined.