I suspect this issue is caused by what is known as "DLL Hell". The problem is that the WRC DLLs are "COM Objects" that require registration with Windows. Unfortunately the older versions of CAESAR II (like 4.50) self-registered the DLLs each time you ran the WRC module. So following a usage with Version 4.50, the 4.50 DLLs are registered. Now if you run Version 5.10, you're running the 5.10 WRC module with the 4.50 DLLs - not a good thing to do.

You can re-register the 5.10 DLLs without reinstalling the software. Using Windows Explorer, go to the \caesar program directory and just double click the batch file "netuserc2.bat". Assuming you have "administrator rights", this will register the 5.10 DLLs.