Right-click on your Tibia icon and select Properties. In the tab Shortcut, look for the line Target. Leave everything in this line as it is. Only at the end of the line leave a space, then add engine, leave another space and add 0 for DirectX 5.0, or 1 for OpenGL, or 2 for DirectX 9.0. If you are in doubt which graphics engine to use, try out which option works best for you.
Make a shortcut of the RX.exe paste it to your desktop or the same folder.
Then you right click the shortcut and go to properties and after "\RW.exe" add one of this and check if its solved if not replace the old number with a new number:
0 = directx 5
1 = opengl
2 = directx 9
so add one of the numbers and paste it after example: "\RW.exe" 0