This message occurs when you try to run an application that uses the Runtime License on a computer with the developer installation of FR Engine while the Protection.Developer.dll* library is in <FREngineinstallation folder>\Bin.
The Protection.Developer.dll library is generated automatically when the developer version of FR Engine was installed. This library should only be used for development and it shouldn't be distributed with applications that use the runtime license (see the Distribution → Distribution Kit article in FR Engine Help for details).
This message is also written in protection logs. It is especially helpful if the error messages in your application are hidden.
*Note: In case you use Linux this library is called libProtection.Developer.so.
Remove the Protection.Developer.dll file from the Bin folder or just change its extension. If you ever need to work with the developer license on the same machine, just put the file back into the Bin folder or change its extension back to .dll.