Is the problem still going on? If so please open up RuneMate through command prompt.
- Press Windows + R.
- Type "cmd".
- Type "java -jar " (with the trailing space) in Command Prompt.
- Then drag and drop RuneMate.jar into Command Prompt. It should now say something similar to "java -jar C:\\Users\You\Downloads\RuneMate.jar".
- Press Enter.
- Login to RuneMate and screenshot Command Prompt after you get the "Cannot connect to server" error.