This problem may occur when Maxthon and Microsoft Internet Explorer 7(IE 7) coexist on your OS.

Solution 1: Uninstall IE 7, and reinstall IE 6.

Solution 2: Modify your registry by steps below:
1. Create a new text file.
2. Copy the codes in red below to the text file: 
Windows Registry Editor Version 5.00

"Maxthon.exe"=dword:00000000
3. Choose “File > Save as”, save this file as a Windows Registry File (*.reg).
4. Double click this file, and merge it into your system registry.
5. Restart your computer.