iPhone cannot be synced because there is not enough free space to hold all of the selected items I'm trying to clean up some space on my iPhone, for this I need to sync it with a new Mac.
The Mac doesn't have the files on the device, so sync will erase everything on the device.
So I want to backup first, and then sync.
But the backup complains there's not enough space (where? Mac has 55GB free).
Errrrr. Pretty stuck here!

This is the message I get from iTunes (12.3.0.44) when trying to manually backup my iPhone 4S (iOS 8.1.2)
to my Mac (Mac Book Pro Yosemite 10.10.5).

This is what happened until now:


Last sync was on another computer (old Windows laptop), this is the
first time trying to backup/sync on this Mac 
iPhone is full (I want
to backup the data and then to cleanup) 
Mac has 55GB free space
Backup wouldn't start, reported not enough space (a different
message!) to sync 
Cleaned the lockdown folder as suggested by Apple
Backup had started but reported an error about a "session could not
be started" 
Restarted the device while connected to Mac (as
suggested on some forum) 
Backup had started but reported this
message ("iPhone XXX cannot be synced because there is not enough
free space to hold all of the selected items.")


Any ideas?

EDIT 2017: I no longer use this phone, eventually I didn't find a solution.
When you start syncing your iDevice in iTunes and then you get this annoying message (especially when it tells you it needs like 1.4MB and there is 300MB available?!): 'The iPhone/iPad “iPhone(insert name)” cannot be synced because there is not enough free space to hold all the selected items'. What do you do?

Basically the problem, in many cases, seems to be that iTunes thinks it has too many updates to install on your iPhone/iPad and it isn't smart enough to load them one at a time when there's not enough space to do them all??

Fortunately it can often be side-stepped by just taking your iPhone/iPad and clicking on the App Store app,  then tapping on the Updates tab, and then tapping on 'Update All' at the top right. If that  complains that there's not enough space you can let do some updates then try again (and again) and will update the rest of the apps. Then the sync should be fine with iTunes.