I'm using three Victron Quattro 48/10000/140-100/100 installed in parallel. Each of them are connected with self-made UTP Cat 5 cables in daisy chain configuration. When I tried to connect the inverters from VEconfigure, the software says "MK3 detected" but after loading for a few seconds, an error message appears which says "error during communication". Any idea what the problem is and how I can solve it? Thanks. 
You need to use "VE.Bus Quick Configure" or "VE.Bus System Configurator" to setup a multi-phase or parallel system.
https://www.victronenergy.com/live/ve.bus:manual_parallel_and_three_phase_systems
If you don't know what you are doing ask someone who does.
A lot of communication problems are caused by self-made UTP cables. Have you tried a high quality factory made cable ?
Jens
Your problem can be trouble shooted by first checking the RJ45 cables.
Victron strongly reccommends using manufactured cables and not self made cables.
Ive seen previous responses which confirm this.
The DC negative of all Quatros in the system must be connected together BEFORE connecting the VE.Bus cable to avoid damage to the data ports.
Make sure you did NOT install the VE.Can terminators to the VE.Bus.
Not sure the length of your cable, but try the shortest one that will work in your system.
You may need to use VE.Bus System Configurator FIRST in a multi Quatro system.
Take the on-line training for multiple Multi/Quatro systems for more helpful clues. This training is on professional.victron.com
Thanks for the advice. The DC negative of all quattros are connected together and I'm not installing VE.Can terminator to VE.Bus.
When I tried connecting to only one quattro with the exact same cable + MK3 converter, it worked. So, it just doesn't work when three quattros are connected.
Is it possible to program each quattro. and operate the system without the VE.bus communication cable connected between three quattros?
NO!!!
Multiple inverter systems MUST be interconnected with VE.Bus so they can function as a single unit. Running each independently would not allow them to synchronize phase. The result could be "interesting" or "explosive".
Take the training I recommended above. It explains much.
