If you're using another software for managing mobile phones, it is recommended to shut it down before attempting to establish a connection through MOBILedit.
If there is such software running, you will be notified by the Connection Wizard.

This dialogue can help you to close the concurrent application. It
 is recommended to close the application the usual way to prevent a data
 loss. If you are sure, that the application doesn't conflict with 
MOBILedit, you can ignore this warning and carry on by clicking the 
Next button (advanced users).
Note: Microsoft Active Sync / Sync Center does 
not restrain MOBILedit from working properly. On the contrary, these 
are required for connection of Windows Mobile based smartphones. To 
learn how to connect a Windows Mobile based smartphone, please proceed 
to the section Connecting a Windows Mobile device.
iTunes has to be installed in order to connect an iPhone / iPod (or any other Apple device) because of the required drivers. However, it should not be running when using MOBILedit. To learn how to connect an iPhone, please proceed to the article Connecting an iPhone.