Repetier-Host connects to printer -- Repetier-Server won't

Hi. After some successful tests of the Server from an old Win7 system, I'm trying to move to a Linux system that is much faster. Host and Server both installed fine. Host accesses the printer fine directly over the /dev/ttyUSB0 connection. However, even though Server is running (obviously, I test this when Host isn't connected!) Server does not appear to communicate with the printer at all (e.g., no LED activity on the printer board). I can access Server on that system via a local or remote browser (or via Host locally or remotely), but no matter what I do there's no evidence of Server even trying to talk to the printer on that USB port (and dmesg confirms it is the correct port). Yet again, Host can talk to that printer perfectly well from the same system on /dev/ttyUSB0. Any ideas? Thanks!

I found it. Needed:

chmod 666 /dev/ttyUSB0

Hey guyss this is my first post and I need someone's help.

Build a Prusa i3 (Anet a8) and all went well.
Printer ran great using the SD card and so I finally connected to the printer with MatterHackes and it did great.
I downloaded arduino and Marlin and was setting up for bed leveling and went to download a firmware and it would not connect.
I went back to MatterHackes and it wouldn't connect also.
Now I have tried just about everything I can think of.
I am running Windows 10 and it seemed to work just fine.
I have changed cables, checked all wiring connections, changed com ports as was available, changed baud rates from 115200 to 2500000 back and forth nothing works.
Down loaded RepRap, Ponter, nothing worked.
I have tried many things I have found on the internet and no luck.
I am about out of idea's and need some different directions, any help would be much appreciated.

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By Gum

Resolved part of my problem.
Decided to grab my lab top and try to see if it would work or the problem was in the printer.
Loaded up MatterHackers program and it connected without a problem, downloaded a print and it did its thing.
Going to try arduino upload later to see if this was part of the problem.
So far so good.
Looks like the problem is in my desktop computer setup and I could still welcome any help that would help resolving the problem.
Going to try and do some compairisons later today.
Will post the differences if found and what the problem was.
Please inject any ideas you may have.

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By Gum

You need to stop Repetier Server before using other programs that need the comport the server is using for the printer.