I experienced the following error with the SimConnect.dll:

An add-on for a DIS interface was moved from the development computer to a test computer with an installed ESP on it. The files were the add-on executable, the SimConnect.dll and the manifest file. This combination worked fine on the development computer. On the test machine I always get the error message that the entry point for SimConnect_Close cannot be found and the add-on terminates immediately. I observed this error in the past when the manifest file was not available. But it is definitely there. The curious thing is, when I delete the line with the call to SimConnect_Close, the add-on works. Does anybody have an idea?