Unable to mount more than 1 device

[comscience15]

I tried to do ideviceimagemounter for second or more device but always got

ERROR: stat: DeveloperDiskImage.dmg.signature.signature: No such file or directory

Do you have a way to mount a second or more device in the same mac or unmount the existing one before remount the second one? The error occur even using the same or different version in DeveloperDiskImage. However, the first device that is mounted is working fine even after reboot mac.