Devices which mount using MTP/PTP (no drive letter allocated)
Note that starting with SyncBackPro/SE V7, MTP devices are supported natively. This article is for SyncBackFree and V6 or older users only. SyncBackPro/SE V7 and newer also supports SyncBack Touch, so you can also install SyncBack Touch on the device to access its files.
Users of mobile phones, tablets and similar devices are reporting that their devices' internal storage (also, any additional/optional internal storage such as an SD card) mount(s) via USB in such a way that the devices (and/or cards, etc.,) are no longer allocated a drive letter by Windows when connected. They mount instead as a 'portable device', with an entry in the Explorer 'tree' below the last allocated drive letter, in a similar location to Network and other resource categories. This is because the devices themselves now only connect (by default, anyhow) using Media Transfer Protocol (MTP) and/or the similar Picture Transfer Protocol (PTP), instead of connecting as a Mass Storage Class (MSC) device, such as a USB drive, flash drive, etcetera. SyncBackFree/SE/Pro V6 cannot currently connect to such devices natively.
What to do in the meantime?
It is possible in some cases (with some devices) that they may have a hidden 'alternate' USB connection mode which does mount the storage as one or more drive letters. You would need to consult your device documentation - and/or other support resources such as user forums for the devices in question - for details. An example of one such alternate mode available with an Android device (Samsung Galaxy S2 with Ice Cream Sandwich OS) is mentioned here:
Go to Menu > Settings > Wireless & Network > More (settings...) > USB Utilities > Set USB Cable Connection Mode
Note that using such an alternate USB mode may disable other functionality on the device (potentially including web access, telephony, etc.) whilst that USB mode is in use.
Alternatively, it may be possible to sidestep the problem of 'no drive letter' by communicating using a different protocol altogether. One possibility is to use (S)FTP, if your device has an (S)FTP server, or you can obtain and install such a server on your device.
Note that 2BrightSparks cannot offer technical support on obtaining, installing or configuring such software, either on the device itself or any supporting utilities on the PC. Any technical support can only be provided once connection is established and files can be transferred using any other (S)FTP client. You should beware especially any bugs or limitations in the (S)FTP server whereby it cannot correctly set the LastModified date/time of files that are transferred to it (and/or, correctly report such properties). Many FTP servers have such limitations, and they will severely impact on any synchronisation process. If files are stamped by default as 'date/time of transfer' they will never match the properties of the files on 'the other side', likely triggering constant re-copying, and/or overwriting 'back' from device to PC (because the files on the portable device now look 'newer' than where they were copied from).
Guidance on obtaining and configuring such 3rd-party software may be available from other forum users, but 2BrightSparks naturally cannot guarantee a response by other users to such queries.