This is a known problem that users who posses the MMX353G 3G modem have issues with the modem explorer. Completely remove the application, drivers, and anything that belongs to this modem. After this procedure, run CCleaner to remove obsolete registry entries and files. Reboot the PC and install the modem again with all its drivers and applications, etc.
After extensive searching, the software appears to have some bugs, therefore I recommend reinstalling it, then apply a compatibility tweak on the main Modem Explorer application. Right click the executable file, then use Properties > Compatibility. Use another version of Windows from the drop down menu and try running it again.