Try searching the system for the DLL, check that the PATH configured for each version includes an entry to include the directory for the DLL. You can open a command prompt and use the "set" command to get the current environment settings dumped in the window, look for "PATH" and check the entries.
"DLL Not found" means the DLL is not installed or not on the PATH, "entry point not found" means that the wrong version is being found. (It may indeed not be installed correctly)
You could also check that the PATH in Control Panel>System, Advanced tab, Environment Variable, System Variables only contains references like "%CDSROOT%\tools\..." and not any absolute directories to the product installations, otherwise changing CDSROOT won't switch all the directory values in the PATH.