This is the solution I found which works correctly:

• Make sure that eclipse is not active. If it is active kill eclipse from the processes tab of the task manager
• Open %USERPROFILE%/ on Windows or simply ~ on Linux/OS X (You can locate this folder from the Desktop)
• Go to .android folder (This may be a hidden folder)
• Delete the folder cache which is located inside .android folder
• Delete the file ddms.cfg which is located inside .android folder
• Start Eclipse

Buon lavoro.