This message occurs when you try to run an application that uses a Runtime license on a computer with the Developer installation of FineReader Engine or another SDK product while the Protection.Developer.dll* library is in <SDK installation folder>\Bin.
The Protection.Developer.dll library is installed automatically when the Developer version of FineReader Engine or other SDK product is installed. This library should only be used for development and it should not be distributed with applications that use a Runtime license (see the Distribution > Distribution Kit articles in Online Help files for the corresponding product for details).
This message is also written in protection logs. It is especially helpful if the error messages in your application are hidden.
Remove the Protection.Developer.dll* file from the Bin (or Bin64) 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 (or Bin64) folder or change its extension back to .dll.
*Note: For FineReader Engine 12 for Linux this library is called libProtection.Developer.so.