This message usually means that you have installed the wrong version of NETePay 5.0. Datacap has released an updated version of NETePay (version 5.03) which should only be installed for specific customer needs. Only install this version if the version notes include an option that the customer is using. Otherwise you should only be downloading version 5.02. If in doubt always install 5.02 and if issues with compatibility arise, you can install the newer version later.
If you are getting this error you will need to completely uninstall the version 5.03 and then install version 5.02.